De-duplicate Level Complete sequence textboxes

Every Level Complete sequence is the same copy-pasted thing, but with
minor changes. To make my work easier, I'm de-duplicating them so I have
less text boxes to change later, and less grind to grind.

desktop_version/src/Game.h

@@ -129,6 +129,11 @@ public:
 
     void gethardestroom(void);
 
+    void levelcomplete_textbox(void);
+    void crewmate_textbox(const int r, const int g, const int b);
+    void remaining_textbox(void);
+    void actionprompt_textbox(void);
+
     void updatestate(void);
 
     void unlocknum(int t);