[Feature Request] Allow custom hotkey to be set per browser

[molohov]

Right now, the number keys 1..9 are the only ways to select browsers from the keyboard, assuming the chooser appears. The numbers are chosen based on the order of the browsers in the list, and are therefore opaque to the user (though specified on the manual)

I think the ability to set a specific hotkey per browser would be nice and clear. For example, browser 1 could be selected with D, and browser 2 could be selected with F, for example.

[mortenn]

I've implemented the basics in the attached branch, but missing user interface to set it up