Browse all access albums in my library fixed + sorting case insensitive + other small fixes

This changeset fixes the browsing of albums in my library. So if you add an album to your library through the Google Music web interface, it will now properly show and play all tracks from it.
All sorting in the plugin is now done case insensitive.
Also the albums in the all access menu are now sorted, where they weren't before.
Fixed warnings in sorting when some fields that are returned from the Google Music service are not always present, like the album year.