Add a way to emulate the GUIDE button

[Drakulix]

Many moonlight platforms (like Android TV or Apple TVs) will capture the GUIDE button of an attached controller. It would be nice if wolf provided a way to translate a weird combination like Hold select for 5 seconds or Start+Select into this button to bring up the Steam Overlay for example more easily.

[shocklateboy92]

Also, current Xbox/Playstation controllers have a dedicated "SHARE" button that doesn't get used for anything. That would be a great candidate to map to GUIDE.