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/items/parts/ItemMultiPart.java

@@ -33,7 +33,7 @@ import cpw.mods.fml.relauncher.SideOnly;
 public class ItemMultiPart extends AEBaseItem implements IPartItem, IItemGroup
 {
 
-	class PartTypeIst
+	static class PartTypeIst
 	{
 
 		PartType part;