[Frontend] IN-PROGRESS Major restructuring of /platform/commonUI/ to add themes structure

open #95
New themes bundle files, .scss and directories;
Moved constants definitions (mainly colors) from commonUI/.../_constants
to individual themes _constants files;
tweaks to mixins files;
changed pathways to font and images in commonUI/.../_constants;

platform/commonUI/themes/snow/res/sass/_controls.scss

@@ -0,0 +1,7 @@
+.s-btn {
+    &.major {
+        $bg: $colorKey;
+        $fg: lighten($bg, 70%);
+        @include btnSubtle($bg, $fg, $fg, 0);
+    }
+}