gitadora: (arena model) single window mode + subscreen overlay (#486)

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

## Description of change
This is a work in progress.

What works:
- [x] subscreen overlay shows the touch screen image (in windowed mode)
- [x] touch works in the overlay
- [x] only the main window is shown, other windows are not launched

What doesn't:
- [ ] game occasionally crashes when entering test menu?
- [ ] full screen mode is not tested at all due to monitor requirements
- [ ] need more polish (various options to control the behavior)

src/spice2x/overlay/windows/exitprompt.cpp

@@ -3,6 +3,7 @@
 #include "misc/eamuse.h"
 #include "util/logging.h"
 #include "games/iidx/iidx.h"
+#include "games/gitadora/gitadora.h"
 
 namespace overlay::windows {
 
@@ -69,6 +70,8 @@ namespace overlay::windows {
             sub = "Show Valkyrie Subscreen";
         } else if (avs::game::is_model("REC")) {
             sub = "Show DRS Dance Floor";
+        } else if (games::gitadora::is_arena_model() && games::gitadora::ARENA_SINGLE_WINDOW) {
+            sub = "Show GITADORA Subscreen";
         }
 
         build_button(this->overlay->window_sub, sub, size, NextItem::NEW_LINE, false);