Allow arrow key controls for the YouTube scrubber

HP2 doesn’t seem to support using the arrow keys to seek through a tab’s attached YouTube video. This is much more pronounced, since the seeker can stick to the mouse cursor if you’re trying to have the seeker begin playback at the very beginning of the video (0:00).

In HP1, the left and right arrow keys work to seek the video playback forward and back 5 seconds, respectively. This makes having the song section actually begin with the beginning of the video much easier: While the video is paused, press left until the seeker is at 0:00, then press [ to lock in the beginning of the section. This is not possible in HP2.