Some performance or memory optimizations

Replaced String concat in loops with StringBuilder (performance)
Replaced for with keySet + Map.get() through for with entrySet (perf)
Changed inner classes to static classes, mostly struct like (memory)

src/main/java/appeng/client/gui/widgets/GuiImgButton.java

@@ -33,7 +33,7 @@ import appeng.core.localization.ButtonToolTips;
 public class GuiImgButton extends GuiButton implements ITooltip
 {
 
-	class EnumPair
+	static class EnumPair
 	{
 
 		final Enum setting;
@@ -63,7 +63,7 @@ public class GuiImgButton extends GuiButton implements ITooltip
 
 	}
 
-	class BtnAppearance
+	static class BtnAppearance
 	{
 
 		public int index;