Category: Add #articles mapping.

Change-Id: Iac78840f98950fc9d79bbbc802baf4ecc961f8b4
diff --git a/src/main/java/eu/mulk/mulkcms2/pages/Category.java b/src/main/java/eu/mulk/mulkcms2/pages/Category.java
index 06e2429..31a9db7 100644
--- a/src/main/java/eu/mulk/mulkcms2/pages/Category.java
+++ b/src/main/java/eu/mulk/mulkcms2/pages/Category.java
@@ -31,4 +31,7 @@
 
   @ManyToMany(mappedBy = "supercategories", fetch = FetchType.LAZY)
   public Set<Category> subcategories;
+
+  @ManyToMany(fetch = FetchType.LAZY, mappedBy = "categories")
+  public Set<Article> articles;
 }