Add ability to change shortcut keys

[Gin-no-kami]

Add the ability to set the shortcut for "already known" and "show additional focus morph" in the settings of morphman (can also include the other two shortcuts as well).

Reason: Having the "K" and "L" keys being the ones used for this results in a number of misclicks when going through new words (specifically meaning to hit L to see other cards but accidentally hitting K). Even after undoing the "focus morph" is buried for the remainder of the day, which is an annoyance. By allowing the user to set their own shortcut, the user will be able to avoid behavior like this.