gitadora: (arena model) headphones i/o (#485)

## Link to GitHub Issue, if one exists
#477 

## Description of change
Plumb through headphone jack detection. Touch screen menu for headphone
volume lights up.

## Testing
Tested guitar.

src/spice2x/games/gitadora/io.cpp

@@ -10,6 +10,7 @@ std::vector<Button> &games::gitadora::get_buttons() {
                 "Service",
                 "Test",
                 "Coin",
+                "Headphone",
                 "Guitar P1 Start",
                 "Guitar P1 Up",
                 "Guitar P1 Down",