[frontends] Custom keybindings

[michaelBelsanti]

As far as I can tell, there is not currently a way to change the built-in controls, such as the ones for moving up and down in the search. I personally use super+j/k for navigating vertical menus, and I think this would be a beneficial feature to add.

I could've missed something and this is already possible, but I'm not sure.

[YalandHong]

Related to #502. But your feature request is more general.