Camera image display

[dmiklic]

Enable camera image display in the GUI, through gstreamer.

[stribor14]

Partialy implemented in 22050a8

[dmiklic]

Ok, looks good so far, but needs to be adapted to work with different camera streams. Stream parameters should be provided thorugh the Settings dialog (expanded with tabs as described in #51)

[dmiklic]

After initially turning the camera on, togglig it off and on again causes the following error:

libv4l2: error setting pixformat: Device or resource busy

and the video stream is not restarted.

[stribor14]

I hope that error is caused by libv4l2 library because same error can be found on the internet by other developers using that library. Needs additional testing.

Currently process is released when GUI is closed (if its terminated in debug mode, user has to kill process which uses libv4l2 manualy from terminal)