main: Add 0-9 keys as shortcuts to seek to 0-90%

Add keyboard shortcut for Numbers 1 to 9 (not on the numeric pad) to
seek to the 10% to 90% of the video.

As used on YouTube:
https://support.google.com/youtube/answer/7631406?hl=en

Closes: #466
2 jobs for master in 14 minutes and 8 seconds (queued for 5 seconds)