Add script to change configuration

[petrockblog]

See https://retropie.org.uk/forum/topic/433/esc-and-f1-keys/5:
Another excellent feature request would be the ability to switch between gamepad mode and keyboard mode on a per emulator or per game basis via something like the runcommand menu.

Arcade/gamepad mode works great for libretro cores, and a custom key-mapped mame/keyboard mode would work great for DOSBox and ports!