Redo capture device selection

[dronus]

There are several issues to capture device selection:

1. there is no way to select devices by their name or something
2. selected devices may fail if they do not support the resolution set by resolution filter. There is no error notification, just a black picture.
3. the device may provide a default resolution that is then used for the whole rendering, if no resolution setup is present. This is a cool if one does not know which resolutions are actually supported. But it is not obvious and may choose low default resolutions despite higher ones availabe.
4. there is no way to reliable choose an audio device mounted to some camera device.

We may solve 1. and 4 in some kind, if audio and video capture devices both show their device names, in which case the user can guess their dependency.
We may solve 2. and 3. by adding a resolution config to the captue filter itself and provide a list of possible resolutions provided by the device.

[dronus]

Also see older issue #7 solved by this.

[dronus]

03aa09f addresses 1) and 4) .

[dronus]

#15 merged. Addressed 1) and 4).