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/core/features/registries/WorldGenRegistry.java

@@ -9,7 +9,7 @@ import appeng.api.features.IWorldGen;
 public class WorldGenRegistry implements IWorldGen
 {
 
-	private class TypeSet
+	private static class TypeSet
 	{
 
 		final HashSet<Class<? extends WorldProvider>> badProviders = new HashSet<Class<? extends WorldProvider>>();