Minor change.
Added crashlytics file to .gitignore.
Merge branch 'GLES2-AnchorCenter' of github.com:nicolasgramlich/AndEngine into GLES2-AnchorCenter
Added ReadWriteLock to SecureSharedPreferences.
Fix issues with GLScissorStack

There were two issues in current implementation:
- original clip rects where kept on stack, instead of clipping intersections
- when popping topmost frame nothing happened (we should return to previous
clip intersection)