Reorganizes asset file structure

Separates assets into
- Source assets: `assets`
- Compiled assets: `dist`

Edits assets.php to reflect changes

Removes '.min' from filenames

Fixes:
- removes 'clean' from build step.

assets/styles/main.less

@@ -0,0 +1,19 @@
+// Bootstrap
+@import "_bootstrap";
+
+// Variable overrides and custom variables
+@import "_variables";
+
+// Roots
+@import "_global";                   // Base styling & custom mixins
+@import "components/_buttons";       // Button tweaks
+@import "components/_forms";         // Form tweaks
+@import "components/_media";         // WordPress media
+@import "components/_wp-classes";    // WordPress generated classes
+@import "layouts/_general";          // General styling
+@import "layouts/_header";           // Header styling
+@import "layouts/_sidebar";          // Sidebar styling
+@import "layouts/_footer";           // Footer styling
+@import "layouts/_pages";            // Page styling
+@import "layouts/pages/_home";       // Home page styling
+@import "layouts/_posts";            // Post styling