Add a protocol / CaptureDevice that generate RGB frame that create
a fading from white to black to white...

Also add a custom MediaDevice for convenience to create a CaptureDevice
with different dimension and/or framerate than the default ones.
Fix some code conventions errors, comment errors.
Remove duplicate code by refactoring the constructor of VideoGreyFadingMediaDevice.
Merge pull request #10 from Haerezis/greyfading

Add a protocol / CaptureDevice that generate RGB frames