Expose image stabilization for AVCaptureStillImageOutput

[eliburke]

Logan, thanks for your work on this wrapper. I've got a suggestion for an improvement. I didn't think a PR was necessary as it is pretty straightforward:

In the header file: @property BOOL isStabilizedMode;

In setup after the AVCaptureStillImageOutput object is created: if (isStabilizedMode && _stillImageOutput.isStillImageStabilizationSupported) { _stillImageOutput.automaticallyEnablesStillImageStabilizationWhenAvailable = YES; }

This is iOS7+, so if you support older code bases it should be wrapped in a respondsToSelector