start splitting up tsb; fix a wtf in the save code

OpenRA.TilesetBuilder/Template.cs

@@ -0,0 +1,19 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenRA.TilesetBuilder
+{
+	class Template
+	{
+		public Dictionary<int2, bool> Cells = new Dictionary<int2, bool>();
+
+		public int Left { get { return Cells.Keys.Min(c => c.X); } }
+		public int Top { get { return Cells.Keys.Min(c => c.Y); } }
+
+		public int Right { get { return Cells.Keys.Max(c => c.X) + 1; } }
+		public int Bottom { get { return Cells.Keys.Max(c => c.Y) + 1; } }
+
+		public int Width { get { return Right - Left; } }
+		public int Height { get { return Bottom - Top; } }
+	}
+}