WIP: animate opening/closing folders with Velocity.js
Animate closing sidebar folders with Velocity.js.
When opening a folder, automatically close any other open folder.
Removed outdated comment.
Removed unnecessary CSS class "closed-folder".
When setting the currently open folder, if the passed folder is already the one currently open one, no action is necessary.
When opening/closing entries, give priority to the animations before making any changes in the angularjs model layer.

The reason is that the animations are what the user is most aware of, and it makes sense priorizing them to achieve a better UX.
When opening a folder, the check to see if any action is necessary is based in comparing folder IDs, not folder objects.

The reason is that folders may be reloaded from the server (e.g. when a feed is moved to a new folder) which creates a new collection of folder objects in memory. In this circumstances we must compare IDs to see if two objects represent the same folder; comparing the objects themselves could give a false negative if one folder object was loaded on page load, and the other one was loaded from the server at a later time.
When a folder is marked as open in the angularjs model layer, it immediately has the "open-folder" CSS class.

This way folders inserted by angularjs are immediately displayed as open, if angularjs knows the folder is open.
Rotate folder arrows when opening/closing using Velocity.js instead of CSS transitions.
Remove unnecessary margin-top animation for folder arrows.

A 1-px animation was imperceptible.
Merge branch 'velocity-open-folder' of github.com:amatriain/feedbunch into velocity-open-folder

Conflicts:
	app/assets/javascripts/ng-services/ng-AnimationsSvc.js.coffee
	app/assets/javascripts/ng-services/ng-OpenFolderSvc.js.coffee
	app/assets/stylesheets/partials/_sidebar.scss
	app/views/read/sidebar/_sidebar_folder.html.erb