view: Add songs list view to Playlists view
grilo: Check for grilo filesystem plugin
grilo: Add method to get a media object from uri
playlists: Add new method for getting path to a playlist
playlists: Add method for parsing playlists
grilo: Connect signals to registry first before loading plugins
playlists: Skip unexistent files
view: Load songs of playlist when selected
view: Monitor playlist songs
view: Update model when current track changes
grilo: Use synchronous get_media_from_uri

The async one causes segmentation faults.
view: Play song when activated
window: Slide out playlist list on Playlists view
po: Add playlist ui files to POTFILES.in
view: Load cached playlist if selected again