move some more (gameplay related) widgets into mods/

OpenRA.Game/Graphics/Minimap.cs

@@ -17,7 +17,7 @@ using OpenRA.Traits;
 
 namespace OpenRA.Graphics
 {
-	class Minimap
+	public class Minimap
 	{		
 		public static Bitmap TerrainBitmap(Map map)
 		{

OpenRA.Game/Graphics/Sheet.cs

@@ -20,7 +20,7 @@ namespace OpenRA.Graphics
 		ITexture texture;
 		bool dirty;
 
-		internal Sheet(Size size)
+		public Sheet(Size size)
 		{
 			this.bitmap = new Bitmap(size.Width, size.Height);
 		}

OpenRA.Game/Graphics/Sprite.cs

@@ -22,7 +22,7 @@ namespace OpenRA.Graphics
 
 		readonly float2[] uvhax;
 
-		internal Sprite(Sheet sheet, Rectangle bounds, TextureChannel channel)
+		public Sprite(Sheet sheet, Rectangle bounds, TextureChannel channel)
 		{
 			this.bounds = bounds;
 			this.sheet = sheet;