Move Blender Cloud specific Sass files to blender-cloud repository

Three Sass files have been moved so far:
_welcome
_homepage
_services

The '_stats.sass' file is no longer used since Kibana

src/styles/main.sass

@@ -4,15 +4,10 @@
 
 /* Generic styles (comments, notifications, etc) come from base.css */
 
-/* Blender Cloud specific styles */
 @import _project
 @import _project-sharing
 @import _project-dashboard
 @import _user
-@import _welcome
-@import _homepage
-@import _services
-@import _stats
 @import _search
 @import _organizations