Features banshee

This is the updated merge request from Launchpad: https://code.launchpad.net/~daschuer/mixxx/features_banshee/+merge/90381

Rating is displayed now and I have added the new Grouping and Album Artist columns.

RJ has commented that it would be nice to duplicate the Banshee Library in the Mixxx database, to be in line with the other external features.
I have not done it yet, because IMHO this is a low priority task for me. I am also in doubt if this will be the right approach, because we have the whole tables in memory as well (BaseTrackCache). The current approach will be in line with the iPod and possible future mpd solution, both provides an in memory linked list.
IMHO it dos not make sense to store this in the mixxx db and than read it back in memory by BaseTrackCache.