Renamed coffeescript file for more homogeneous nomenclature.

Now we speak about "moving a file into a folder" instead of "adding a file to a folder".
Moving a feed into an existing folder is requested with an HTTP PATCH, instead of a PUT.

This takes advantage of Rails 4 support for the PATCH HTTP verb. PATCH is more correct when submitting a partial representation of a resource.

Moving a feed into a newly created folder is still done with a HTTP POST, because it's correct for creating a new resource instance.
Removing a feed from its folder is requested via an HTTP PATCH request, instead of a DELETE request.

The path for this PATCH request is the same as when moving a feed to an existing folder, and it's routed to the FoldersController#update RESTful action. The difference is that when removing a feed from a folder the folder id passed as a parameter is "none".

The custom named route "folder_remove" has been deleted along with the FoldersController#remove action. Only normal RESTful routes and controller actions are used now for folders.