Added user-group name pattern (issue #33).

Change-Id: I578592045d0e64c2daf4cdfdb2df1d4659629820
diff --git a/core/src/main/java/de/ids_mannheim/korap/exceptions/StatusCodes.java b/core/src/main/java/de/ids_mannheim/korap/exceptions/StatusCodes.java
index a8cba15..bd4bf89 100644
--- a/core/src/main/java/de/ids_mannheim/korap/exceptions/StatusCodes.java
+++ b/core/src/main/java/de/ids_mannheim/korap/exceptions/StatusCodes.java
@@ -124,6 +124,7 @@
     public static final int INVITATION_EXPIRED = 1605;
     public static final int GROUP_NOT_FOUND = 1606;
     public static final int GROUP_DELETED = 1607;
+    public static final int GROUP_EXISTS = 1608;
     
     /**
      * 1800 Oauth2 and OpenID