overlay: UI scaling option (#495)

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

## Description of change
Add a new option for scaling the overlay.

Gitadora Arena will receive 250% by default.

Various overlay windows have been updated to scale properly, not perfect
but they are at least usable.

src/spice2x/launcher/options.h

@@ -47,6 +47,7 @@ namespace launcher {
             SOFTID,
             VREnable,
             DisableOverlay,
+            OverlayScaling,
             spice2x_FpsAutoShow,
             spice2x_FpsOpposite,
             spice2x_SubScreenAutoShow,