Android: Use QMutexLock in camera callbacks.

We should not release the locks before the native callbacks returns.

Change-Id: Ia2691f6c5be66a3dcf371e48e3bac7498b401833
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Android: Camera code clean-up

Change-Id: Ib400afde12067764c3dcc0f44e40ddc1abb3012f
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>