Universal HeadPhone Holder

Added a headphone holder to failfish's modular controller holder. Print in conjunction with thespasticbastad's Universal Controller Hangar Top Mount https://www.thingiverse.com/thing:4840622 to wall mount it, or use 3m strips as Failfish did. Will be creating a spacer that fits this modular build later as well, to give room between controllers and headphones (or just print a blank one).