Add MapGrid class

MapGrid is a mod Manifest field which includes (and thus makes redundant) TileSize, TileShape, SubCells info and MaximumTerrainHeight.

OpenRA.Game/Map/ProjectedCellRegion.cs

@@ -42,7 +42,8 @@ namespace OpenRA
 			// been projected into this region if they have height > 0.
 			// Each height step is equivalent to 512 WRange units, which is one MPos
 			// step for diamond cells, but only half a MPos step for classic cells. Doh!
-			var heightOffset = map.TileShape == TileShape.Diamond ? map.MaximumTerrainHeight : map.MaximumTerrainHeight / 2;
+			var maxHeight = map.Grid.MaximumTerrainHeight;
+			var heightOffset = map.Grid.Type == TileShape.Diamond ? maxHeight : maxHeight / 2;
 
 			// Use the MapHeight data array to clamp the bottom coordinate so it doesn't overflow the map
 			mapBottomRight = map.MapHeight.Value.Clamp(new MPos(bottomRight.U, bottomRight.V + heightOffset));