Reduces visibility of internal fields/methods

Reduces the visibility of all fields to private and create setters/getters
when necessary. Exceptions are fields with GuiSync as these need to be
public.

Reduces the visibility of internal methods to private/protected/default when possible.

src/main/java/appeng/core/FeatureHandlerRegistry.java

@@ -34,7 +34,7 @@ public final class FeatureHandlerRegistry
 		this.registry.add( feature );
 	}
 
-	public Set<IFeatureHandler> getRegisteredFeatureHandlers()
+	Set<IFeatureHandler> getRegisteredFeatureHandlers()
 	{
 		return this.registry;
 	}