improve concept docs structure

Author: AndreiKingsley

docs/StardustDocs/c.list

@@ -2,5 +2,5 @@
 <!DOCTYPE categories
         SYSTEM "https://resources.jetbrains.com/writerside/1.0/categories.dtd">
 <categories>
-
+    <category id="related" name="Related topics" order="1"/>
 </categories>

docs/StardustDocs/d.tree

@@ -21,12 +21,19 @@
         <toc-element topic="gettingStartedDatalore.md"/>
         <toc-element topic="gettingStartedGradleAdvanced.md"/>
     </toc-element>
-    <toc-element topic="overview.md">
+    <toc-element topic="concepts.md">
         <toc-element topic="apiLevels.md">
             <toc-element topic="stringApi.md"/>
             <toc-element topic="extensionPropertiesApi.md"/>
         </toc-element>
+        <toc-element topic="types.md">
+            <toc-element topic="DataFrame.md"/>
+            <toc-element topic="DataColumn.md"/>
+            <toc-element topic="DataRow.md"/>
+        </toc-element>
         <toc-element topic="hierarchical.md"/>
+        <toc-element topic="nanAndNa.md"/>
+        <toc-element topic="numberUnification.md"/>
         <toc-element topic="schemas.md">
             <toc-element topic="schemasGradle.md"/>
             <toc-element topic="schemasJupyter.md"/>
@@ -36,20 +43,15 @@
             <toc-element topic="schemasImportSqlGradle.md"/>
             <toc-element topic="schemasImportOpenApiGradle.md"/>
             <toc-element topic="schemasImportOpenApiJupyter.md"/>
+            <toc-element topic="DataSchemaGenerationMethods.md"/>
+            <toc-element topic="DataSchemaGenerationGradle.md"/>
         </toc-element>
     </toc-element>
-    <toc-element topic="types.md">
-        <toc-element topic="DataFrame.md"/>
-        <toc-element topic="DataColumn.md"/>
-        <toc-element topic="DataRow.md"/>
-    </toc-element>
     <toc-element topic="Compiler-Plugin.md">
         <toc-element topic="staticInterpretation.md"/>
         <toc-element topic="dataSchema.md"/>
         <toc-element topic="compilerPluginExamples.md"/>
     </toc-element>
-    <toc-element topic="nanAndNa.md"/>
-    <toc-element topic="numberUnification.md"/>
     <toc-element topic="operations.md">
         <toc-element topic="create.md">
             <toc-element topic="createColumn.md" toc-title="DataColumn"/>
@@ -199,8 +201,6 @@
             <toc-element topic="jupyterRendering.md"/>
         </toc-element>
     </toc-element>
-    <toc-element topic="DataSchema-Data-Classes-Generation.md">
-        <toc-element topic="gradleReference.md"/>
-    </toc-element>
     <toc-element topic="_shadow_resources.md" hidden="true"/>
+    <toc-element topic="Support.md"/>
 </instance-profile>

docs/StardustDocs/images/github-mark.svg

@@ -260,7 +260,7 @@ For instance, excluding `userData.age`:
 `df.select { colsAtAnyDepth { "a" in it.name() } except userData.age }`
 
 Note that the selection of columns to exclude from column sets is always done relative to the outer scope.
-Use the [Extension Properties API](extensionPropertiesApi.md) to prevent scoping issues if possible.
+Use the [Extension Properties API](concepts/extensionPropertiesApi.md) to prevent scoping issues if possible.
 
 > Special case: If a column that needs to be removed appears multiple times in the [`ColumnSet`](#column-resolvers),
 > it is excepted each time it is encountered (including inside [Column Groups](DataColumn.md#columngroup)).
@@ -392,19 +392,19 @@ This function behaves the same as [`cols {}` and `[{}]`](ColumnSelectors.md#cols
 Creates a [`ColumnSet`](#column-resolvers) containing the columns from both the left and right side of the function. This allows
 you to combine selections or simply select multiple columns at once.
 
-Any combination of [AccessApi](apiLevels.md) can be used on either side of the `and` operator.
+Any combination of [AccessApi](concepts/apiLevels.md) can be used on either side of the `and` operator.
 
 Note, while you can write `col1 and col2 and col3...`, it may be more concise to use
 [`cols(col1, col2, col3...)`](ColumnSelectors.md#cols) instead. The only downside is that you can't mix
-[Access APIs](apiLevels.md) with that notation.
+[Access APIs](concepts/apiLevels.md) with that notation.
 
 ##### Rename {collapsible="true"}
 `colA named "colB"`, `colA into namedColAccessor`
 
 Renaming a column in the Columns Selection DSL is done by calling the infix functions 
 `named` or `into`.
 They behave exactly the same, so it's up to contextual preference which one to use.
-Any combination of [Access API](apiLevels.md) can be used to specify the column to rename 
+Any combination of [Access API](concepts/apiLevels.md) can be used to specify the column to rename 
 and which name should be used instead.
 
 ##### Expr (Column Expression) {collapsible="true"}

docs/StardustDocs/topics/ColumnSelectors.md

@@ -20,7 +20,7 @@
         <primary>
             <title>First steps</title>
             <a href="gettingStartedKotlinNotebook.md"/>
-            <a href="overview.md"/>
+            <a href="concepts.md"/>
             <a href="operations.md"/>
             <a href="read.md">Reading from files: CSV, JSON, ApacheArrow</a>
         </primary>
@@ -32,7 +32,6 @@
             <a href="readSqlDatabases.md"/>
         </secondary>
 
-
     </section-starting-page>
 
 

docs/StardustDocs/topics/Home.topic

@@ -0,0 +1,14 @@
+# Support
+
+* <img src="github-mark.svg" alt="GitHub logo" height="24"/> 
+[**Issue Tracker**](https://github.com/Kotlin/dataframe/issues)
+
+   If you find a bug or have an idea for a new feature, 
+   file an issue in our [DataFrame GitHub repository](https://github.com/Kotlin/dataframe).
+
+* <img src="https://kotlinlang.org/docs/images/slack.svg" alt="Slack logo" height="24"/> 
+[**Community**](https://github.com/Kotlin/dataframe/issues)
+
+  Peer-to-peer support is available on the Kotlin Slack
+  [#datascience](https://kotlinlang.slack.com/archives/C4W52CFEZ) channel
+  ([request an invite](https://surveys.jetbrains.com/s3/kotlin-slack-sign-up?_gl=1*1ssyqy3*_gcl_au*MTk5NzUwODYzOS4xNzQ2NzkxMDMz*FPAU*MTk5NzUwODYzOS4xNzQ2NzkxMDMz*_ga*MTE0ODQ1MzY3OS4xNzM4OTY1NzM3*_ga_9J976DJZ68*czE3NTE1NDUxODUkbzIyNyRnMCR0MTc1MTU0NTE4NSRqNjAkbDAkaDA.)).

docs/StardustDocs/topics/Support.md

@@ -1,4 +1,4 @@
-[//]: # (title: Gradle plugin reference)
+[//]: # (title: Data Shemas Generation in Gradle)
 
 This page describes the Gradle plugin that generates `@DataSchema` from data samples.
 ```Kotlin