Interpolate bringing up and down quit/pause/teleporter screen

Now it's really, really smooth. Except for like the last frame when it
goes down, which I sometimes didn't notice (but maybe it didn't happen
every time due to being lucky on the delta timesteps or something,
whatevs.)

desktop_version/src/Logic.cpp

@@ -40,6 +40,7 @@ void maplogic()
     help.updateglow();
     graphics.updatetextboxes();
 
+    graphics.oldmenuoffset = graphics.menuoffset;
     if (graphics.resumegamemode)
     {
         graphics.menuoffset += 25;