Added ability to tag an album

Added the ability to tags an album and to filter a collection by a tag.

The tagging is done via the Collection page by displaying a "Tags" option in the action menu of an album. This allow to add, remove and edit tags.

The filtering is also available via the Collection page with the addition of a "Filter By Tag" textbox. The filtering can be a little slow at the moment as Rdio only partially load the albums of a collection. To be able to display all album associated with a tag, I need to fetch all the albums and then apply the filter. This will obviously be slower with larger collection.