Integrate video into the UI

A video button is shown if the model provides an url for a video.
If the button is pressed the video element is added in a similar way
to the aboutInfo and starts the video directly. Once the playback
stopped a play again button is shown.

If one clicks the video button again, the video gets hidden.

Room for improvement:
* add a button to open in external player
* ensure video is centered correctly in the list view