Fetches the number of tracks contained in a playlist
Highlights the currently played track, by displaying a play icon next to it

Not tested, to be done soon.
Refactorizes SoloMainActivity and its fragments

* Removes unused onPlaylistInfoListener
* Changes visibility of AbstractPlayer.next() from private to default
* Overrides AbstractPlayer.next() in SoloPlayerFragment
* Highlighting the currently played track in SoloTracksFragment doesn't work
* Improves listrow_track: adds an image to the left of the row, to be used to
  highlight the played track

The getListView() count in SoloTracksFragment always returns 0, thus I can't
access the ListView children. I haven't figured out how to overcome this issue
for now, that's why the highlighting doesn't work.

BUG the played track in GroupsPlayer doesn't correspond to the displayed data.
This is probably due to an issue when fetching the track from the DB (wrong
id).
Organizes imports
Formats project
Hides the unused rating stars in tracks list of SoloTracks

Since the RatingBar had the same id in listrow_stats and listrow_track, the
renaming of one RatingBar id had as side-effect to rename the other one. This
conflict is now resolved by two distinct ids.
FIX empty ListView of tracks in GroupsRatings

The tracks are back in the ratings activity. There was an issue with the
comparator (bad instanceof check!?!).

If your tracks are not shown, it is also possible that your database is
empty. The trick is then to reduce the LibraryService.MIN_UPDATE_INTERVAL to a
small value, like 60s (default value is 10h), and restart your AVD.

Commit applies:
* Organized imports
* Formatted project
Merge branch 'dev/solo' of https://github.com/lca4/unison-android into dev/solo
Reduces I/O for AbstractFragmentActivities

* SoloPlaylistsActivity
Since the playlists fetched from the server are only the one created by the
user, there is no need to refresh. The user only accesses his content, so if he
does nothing, nothing happens and there's nothing to refresh.
But there's always the possibility to request a manual refresh by clicking the
refresh button in the action bar.

* AbstractFragmentActivity
  * Auto refresh
A boolean can be set for activities that doesn't request an automated refresh.
  * Default refresh interval
Since the content fetched from the server doesn't change much over time, the
refresh interval is increased from 30s to 60s.
There's always the possibility to request a manual refresh by clicking the
refresh button in the action bar.
Merge branch 'dev/solo' of https://github.com/lca4/unison-android into dev/solo
Merge branch 'master' into dev/solo