Cleanup AVCaptureSession on ZXCapture dealloc

Remove AVCaptureInputs and AVCaptureOutputs from AVCaptureSession on ZXCapture dealloc to prevent delays when those same inputs and outputs are need for further scanning or other frameworks etc.
keep AVCaptureSession start/stop in main thread
Merge pull request #171 from sveltema/master

Cleanup AVCaptureSession on ZXCapture dealloc