WIP: transition to AngularJS.

For the moment I'm rewriting the sidebar partial. Currently it uses a hardcoded list of folders that are painted using angularjs. Next step, retrieve folders JSON from the server via AJAX.
Added FoldersController#index method and RESTful route.

This method returns a JSON list with the folders owned by the current user.
WIP: migration to angularjs. Retrieve the folders list from the server via AJAX.
Added FeedsController#index method and RESTful route. It returns a JSON list of all feed subscribed by the current user.