Qt5 Mac builds. Not 100% perfect, TODO:
- Unified toolbar - appears, but cannot drag on all?
- HighDPI support - pixmaps should be scaled, but are not. Cantata's detection code needs modifying
- Cover in toolbar is a bit too large
- Some odd layout in pref dialog


git-svn-id: http://cantata.googlecode.com/svn/trunk@5329 b1e49159-3266-923f-9c3e-04f16369770a