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/overlay.cpp

@@ -29,6 +29,7 @@
 #include "windows/generic_sub.h"
 #include "windows/iidx_seg.h"
 #include "windows/iidx_sub.h"
+#include "windows/gfdm_sub.h"
 #include "windows/drs_dancefloor.h"
 #include "windows/iopanel.h"
 #include "windows/iopanel_ddr.h"
@@ -410,7 +411,10 @@ void overlay::SpiceOverlay::init() {
             window_sub = new overlay::windows::DRSDanceFloorDisplay(this);
         } else if (avs::game::is_model("KFC")) {
             window_sub = new overlay::windows::SDVXSubScreen(this);
+        } else if (games::gitadora::is_arena_model() && games::gitadora::ARENA_SINGLE_WINDOW) {
+            window_sub = new overlay::windows::GitaDoraSubScreen(this);
         }
+
         if (window_sub) {
             this->window_add(window_sub);
             if (AUTO_SHOW_SUBSCREEN) {