Added grouping of items in sidebar + correct clock placement

Items in the sidebar are now grouped by their type and one of each item in the group can be 'built' at a time. Clock animation is now drawn on the items that are being built. Build time still not implemented. Behaviour after item built not correct.

OpenRa.Game/SidebarItem.cs

@@ -9,8 +9,6 @@ namespace OpenRa.Game
 		public readonly float2 location;
 		readonly Sprite sprite;
 
-		public bool isBuilding = false;
-
 		public SidebarItem(Sprite s, Item item, int y)
 		{
 			this.techTreeItem = item;