Make 'PaginationController' class abstract

src/main/java/de/thm/arsnova/controller/PaginationController.java

@@ -20,7 +20,7 @@ package de.thm.arsnova.controller;
 /**
  * Adds pagination properties to controllers.
  */
-public class PaginationController extends AbstractController {
+public abstract class PaginationController extends AbstractController {
 	protected int offset = -1;
 	protected int limit = -1;