Reduce the size of the sheets created for fonts.

- A 512x512 sheet is about half full after precaching and some usage, but uses 16x less memory than the default 2048x2048 sheet. This saving occurs twice as we maintain a managed buffer for this sheet.
- Only precache smaller fonts, as the larger fonts are less used and take up more space than is worthwhile.
- Only precache in white, as red is largely unused.

OpenRA.Game/Graphics/SpriteFont.cs

@@ -49,8 +49,8 @@ namespace OpenRA.Graphics
 			Func<char, float> characterWidth = character => glyphs[Pair.New(character, Color.White)].Advance;
 			lineWidth = line => line.Sum(characterWidth) / deviceScale;
 
-			PrecacheColor(Color.White, name);
-			PrecacheColor(Color.Red, name);
+			if (size <= 24)
+				PrecacheColor(Color.White, name);
 		}
 
 		public void SetScale(float scale)