add line numbers and code folding

Author: lawson89

sierra-tools/previewer/src/main/java/org/httprpc/sierra/tools/previewer/MainFrame.java

@@ -13,22 +13,16 @@
  */
 package org.httprpc.sierra.tools.previewer;
 
-import org.fife.rsta.ui.search.FindDialog;
-import org.fife.rsta.ui.search.ReplaceDialog;
-import org.fife.rsta.ui.search.SearchEvent;
-import org.fife.rsta.ui.search.SearchListener;
-import org.fife.ui.autocomplete.AutoCompletion;
-import org.fife.ui.autocomplete.CompletionProvider;
-import org.fife.ui.rsyntaxtextarea.RSyntaxTextArea;
-import org.fife.ui.rsyntaxtextarea.SyntaxConstants;
-import org.fife.ui.rtextarea.SearchEngine;
-import org.fife.ui.rtextarea.SearchResult;
-import org.httprpc.sierra.Outlet;
-import org.httprpc.sierra.UILoader;
-import org.httprpc.sierra.tools.previewer.engine.RenderingEngine;
-import org.httprpc.sierra.tools.previewer.model.RenderError;
-import org.httprpc.sierra.tools.previewer.model.RenderResult;
-
+import java.awt.BorderLayout;
+import java.awt.Toolkit;
+import java.awt.event.KeyEvent;
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+import java.util.concurrent.ExecutionException;
+import java.util.function.Consumer;
 import javax.swing.ImageIcon;
 import javax.swing.JFileChooser;
 import javax.swing.JFrame;
@@ -38,7 +32,6 @@
 import javax.swing.JMenuItem;
 import javax.swing.JOptionPane;
 import javax.swing.JPanel;
-import javax.swing.JScrollPane;
 import javax.swing.JSplitPane;
 import javax.swing.KeyStroke;
 import javax.swing.SwingWorker;
@@ -47,17 +40,22 @@
 import javax.swing.event.DocumentEvent;
 import javax.swing.event.DocumentListener;
 import javax.swing.filechooser.FileNameExtensionFilter;
-import java.awt.BorderLayout;
-import java.awt.Toolkit;
-import java.awt.event.KeyEvent;
-import java.io.File;
-import java.io.IOException;
-import java.nio.file.Files;
-import java.nio.file.Path;
-import java.nio.file.StandardOpenOption;
-import java.util.concurrent.ExecutionException;
-import java.util.function.Consumer;
+import org.fife.rsta.ui.search.FindDialog;
+import org.fife.rsta.ui.search.ReplaceDialog;
+import org.fife.rsta.ui.search.SearchEvent;
+import org.fife.rsta.ui.search.SearchListener;
+import org.fife.ui.autocomplete.AutoCompletion;
+import org.fife.ui.autocomplete.CompletionProvider;
+import org.fife.ui.rsyntaxtextarea.RSyntaxTextArea;
+import org.fife.ui.rsyntaxtextarea.SyntaxConstants;
 import org.fife.ui.rtextarea.RTextScrollPane;
+import org.fife.ui.rtextarea.SearchEngine;
+import org.fife.ui.rtextarea.SearchResult;
+import org.httprpc.sierra.Outlet;
+import org.httprpc.sierra.UILoader;
+import org.httprpc.sierra.tools.previewer.engine.RenderingEngine;
+import org.httprpc.sierra.tools.previewer.model.RenderError;
+import org.httprpc.sierra.tools.previewer.model.RenderResult;
 
 /**
  * The main application window for the Sierra UI Previewer. UI is defined in