Make MusicCore non-static
Make MusicCore and other dependencies (MusicDataStoreHandle) non-static
For compatibility, MusicCore still has a singleton instance that is statically instantiated and can be used as needed by legacy users.
These changes should be made in calling sites (legacy users using singleton):
MusicDataStoreHandle.getDSHandle() -> MusicCore.getInstanceDSHandle()
Change-Id: I02b67f316dc21a1498157bc68cc32bf76d3ec01e
Issue-ID: MUSIC-148
Signed-off-by: Mohammad Salehe <salehe@cs.toronto.edu>