add group moderation and banning functionality to api (#13)

* add group moderation and banning functionality to api

* set moderator to false on group migration

* send IsModerator in addition on group join

Co-authored-by: rootdarkarchon <root.darkarchon@outlook.com>

MareSynchronosServer/MareSynchronosShared/Models/GroupPair.cs

@@ -8,4 +8,5 @@ public class GroupPair
     public User GroupUser { get; set; }
     public bool IsPaused { get; set; }
     public bool IsPinned { get; set; }
+    public bool IsModerator { get; set; }
 }