Disable YouTube Number Key Shortcuts (Except 0) per tuure

Notice: this fork is no longer necessary since we added settings to toggle 0 in https://github.com/timmontague/youtube-disable-number-seek/issues/10

Recommended to switch to the original v1.4:

https://addons.mozilla.org/en-US/firefox/addon/youtube-disable-number-seek/

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Fork of https://github.com/timmontague/youtube-disable-number-seek

Doesn't disable 0 so it can be used to go to the start of video, but disables the rest of the numbers.

The original also disables Home/End, but this fork does not, because I find them useful.