Move variable definitions to match Docsy

Put the variable definitions for SCSS where Docsy says they belong.

Author: Tim Bannister

assets/scss/_skin.scss

@@ -2,7 +2,6 @@
 Add styles or import other files. */
 
 @import "reset";
-@import "skin";
 
 //K8S-Docsy integration
 @import "custom";

assets/scss/_styles_project.scss

@@ -3,6 +3,12 @@ Override variables from the theme here. */
 
 $primary: #326ce5;
 
+$blue: #326ce5;
+$light-grey: #f7f7f7;
+$dark-grey: #303030;
+$medium-grey: #4c4c4c;
+$white: #ffffff;
+
 // tooltip
 $tooltip-bg: #555;
 $tooltip-arrow-color: $tooltip-bg !default;