Fixed auto exposure bug in Windows

This was a very hard to catch bug since not all webcams has this control and it was not clear how it was triggered. The bug consisted in Webcamoid turning off all boolean type controls (auto. exposure, auto. focus, etc.) with the exposure control being the most affected one turning the image darker, and since Windows does not provides any native options for setting the controls back, users needed to use 3rd-party programs to fix the problem.

This bug is finally fixed once for all.

Improved FaceDetect plugin

Since this release was more focused on fixing the above bug, I did not wanted to make an almost void release for the rest of the platforms so I've back ported some small but interesting changes from Webcamoid's master branch. And one of those interesting changes is that the FaceDetect plugin can now blur the outsides of the detected faces (PR #332) and the face detection algorithm can be used directly in other plugins (PR #329).

Thanks you very much to Erich Schubert and Chris Barth for this improvement.