Add being able to disable unfocus pause

It's sometimes unwanted by people, and it's unwanted enough that there
exist instructions to hexedit the binary to remove it (
https://distractionware.com/forum/index.php?topic=3247.0 ).

Fun fact, the unfocus pause didn't exist in 2.0.

desktop_version/src/Game.h

@@ -415,6 +415,8 @@ public:
 
     bool shouldreturntopausemenu;
     void returntopausemenu();
+
+    bool disablepause;
 };
 
 extern Game game;