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/components/_wp-classes.less

@@ -0,0 +1,28 @@
+// WordPress Generated Classes
+// http://codex.wordpress.org/CSS#WordPress_Generated_Classes
+
+.aligncenter {
+  display: block;
+  margin: (@line-height-computed / 2) auto;
+}
+.alignleft,
+.alignright {
+  margin-bottom: (@line-height-computed / 2);
+}
+figure.alignnone {
+  margin-left: 0;
+  margin-right: 0;
+  max-width: 100%;
+}
+
+@media (min-width: @screen-sm-min) {
+  // Only float images if not on an extra small device like smartphones
+  .alignleft {
+    float: left;
+    margin-right: (@line-height-computed / 2);
+  }
+  .alignright {
+    float: right;
+    margin-left: (@line-height-computed / 2);
+  }
+}