Added a minimap renderer to OpenRA.Utility.exe

#4195 for http://content.open-ra.org/ which should migrate to this tool. The PNGs generated with it are 10x smaller than the BMP created by https://github.com/Holloweye/OpenRA-Content-Website/blob/master/python/minimap.py It should also fix wrong radar colors for the ARRAKIS tileset etc.