Allow extension brightness to be changed via hotkeys

[NicoForce]

This is an enhancement request, I'd love if this extension had keyboard shortcuts I could use to change the brightness.

[BinaryGenius]

I actually wrote my own little script for brightness control it's nothing special but if you'd like I can send it.

[BinaryGenius]

Also this is a mirror of #38 which I referenced to make the script.

[neuromorph]

Came here to check for hotkeys but ended up doing the same, built a script using dconf commands and added to custom keyboard shortcuts.