Expose map thumbnail and minimap to lua

As title says, let lua access map thumbnail and minimap patches because thats the only way that those can be accessed by lua.

mapheaderinfo[map].thumbnail gives the map thumbnail patch and mapheaderinfo[map].minimap gives the minimap patch. If for some reasons those arent loaded or valid then loads "BLANKLVL" youfuckedup patch as a failsafe

results using simple lua coding to display maps thumbnails and minimaps on screen.