Rework multi-resolution sprite handling:

- Sprite.Bounds now refers to rectangles in the source image.
  Use this when copying pixels, etc.
- Sprite.Size now refers to sizes in effective pixel coordinates.
  Use this when rendering.
- Sheet.DPIScale has been removed.
- "Density" term is introduced to refer to the number of artwork
  pixels per effective pixel.

OpenRA.Mods.Common/Widgets/ColorMixerWidget.cs

@@ -164,8 +164,8 @@ namespace OpenRA.Mods.Common.Widgets
 			Game.Renderer.RgbaSpriteRenderer.DrawSprite(mixerSprite, RenderOrigin, new float2(RenderBounds.Size));
 
 			var sprite = ChromeProvider.GetImage("lobby-bits", "colorpicker");
-			var pos = RenderOrigin + PxFromValue() - new int2(sprite.Bounds.Width, sprite.Bounds.Height) / 2;
-			WidgetUtils.FillEllipseWithColor(new Rectangle(pos.X + 1, pos.Y + 1, sprite.Bounds.Width - 2, sprite.Bounds.Height - 2), Color);
+			var pos = RenderOrigin + PxFromValue() - new int2((int)sprite.Size.X, (int)sprite.Size.Y) / 2;
+			WidgetUtils.FillEllipseWithColor(new Rectangle(pos.X + 1, pos.Y + 1, (int)sprite.Size.X - 2, (int)sprite.Size.Y - 2), Color);
 			Game.Renderer.RgbaSpriteRenderer.DrawSprite(sprite, pos);
 		}