Request: Add Sub-Category for keybindings

[GuzzenVonLidl]

Sub-categories were a great addition to the settings system, so why not at the same time implement it to the key-binding system?

[commy2]

The problem with this is, that the settings use a controls group control, which can contain any other type of control, i.e. unclickable text and single pixel lines, while the keybinds use a listNbox, which only supports clickable list items. I don't see any way to change this without redesigning the keybinding ui.