TVer Unofficial Extension by Michael

* This extension is mainly adding functionality on TVer, a Japanese video on-demand site.

1. Added video player shortcuts:

* Spacebar to play/stop the video
* "F" to fullscreen
* "C" to toggle subtitle
* "M" to toggle mute
* Left arrow and right arrow will rewind and fast forward for 10s respectively
* Pressing Shift key together with left arrow and right arrow will speed up to 30s

2. In addition, horizontal list will be scrollable with mouse wheel and gesture.