Capture and stop propagation of 'tap' event in video viewer

Both Polymer and video.js listen for click/touch event and emit a ‘tap’ event which means listeners on controls were being fired twice (once for the ‘tap’ event generated by video.js and once for the ‘tap’ event generated by Polymer).

fix for now is to listen the 'tap' event in the 'capture' phase and stop the propagation.

To check if it still works on mobile devices.