ofxiOSVideoGrabber made compatible with new API

- replaced initGrabber() with setup()
- replaced getPixelsRef() with getPixels()
- replaced getDeviceList() with listDevices()
- added deprecation messages.
- general cleanup.
Merge pull request #3350 from julapy/ofxiOSVideoGrabber-api-update

ofxiOSVideoGrabber made compatible with new API