Dependency for advanced_help module

Hi! At DrupalCon we talked about having advanced_help as a dependency for CDN so that users don't miss help text necessary for correctly configuring the module.

What we discussed was instead of modifying the current branch, have branch 3 have two modules, cdn and cdn_ui with cdn_ui having a dependency on advanced_help. That way we get the benefit of clear help text without impacting on performance in a production setup.

Thanks!