Improve control of VideoList (gallery of loaded players)

[juergmessmer]

So far the "existing" video list (frontend module method) simply displays a list of loaded videos.
Any video can be played/paused and controlled the way it's expected, except that you can play multiple videos and lose control of which one is playing.

My suggestion how it should work.
• clicking a player should pause/stop all other players in the list, if it is newly selected otherwise it should simply execute the default player actions pause/stop
• the selected player iframe should be highlighted with class "is_active" to optionally visualize the player in action