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.DataStructures/int2.cs

@@ -37,5 +37,6 @@ namespace OpenRa
 		public static readonly int2 Zero = new int2(0, 0);
 		public Point ToPoint() { return new Point(X, Y); }
         public PointF ToPointF() { return new PointF(X, Y); }
+		public float2 ToFloat2() { return new float2(X, Y); }
 	}
 }