Working example of how global keyevents work
VideosController is listening to key presses
A video is now 'displayed' instead of 'selected'

  * This concerns the video that is in the youtube player, no matter if
    it's playing or not
  * This change frees up 'selected' to be used for the keyboard
    navigation aspect
  * Changed the color of the displayed video element to a red
Moving displayedVideo handling into VideosController
Able to select videos with j and k
is_a -> isA
Enter changes the video
Pressing space will play/pause the video
Merge branch 'feature/7-keyboard-controls' into develop