Add Flip Mode to game options if in M&P or in-game menu and unlocked

Flip Mode will now be in the game options menu if either:
 (1) You're playing the M&P version.
 (2) You have it unlocked and you came here from the in-game pause
     screen.

This is because if you're playing M&P, you'd have to close the game,
edit unlock.vvv, and re-launch the game to toggle Flip Mode, since
there's no other way to do so. And if you're playing the full version,
you'd have to save and exit your session in order to toggle Flip Mode.

desktop_version/src/Game.cpp

@@ -7209,6 +7209,12 @@ void Game::createmenu( enum Menu::MenuName t, bool samemenu/*= false*/ )
     case Menu::options:
         option("accessibility options");
         option("glitchrunner mode");
+#if !defined(MAKEANDPLAY)
+        if (ingame_titlemode && unlock[18])
+#endif
+        {
+            option("flip mode");
+        }
 #if !defined(MAKEANDPLAY)
         option("unlock play modes");
 #endif