Circles, pub & auth

* Adds a boolean to each Circle, saying that
  it is public, and its existence may be known by any interested in
* Adds claims of type "YavscClaimTypes.CircleMembership" at
  login, in order to implement some faster authorisation processes and file restricted accesses.

src/Yavsc.Server/Models/ApplicationUser.cs

@@ -109,6 +109,9 @@ namespace Yavsc.Models
         [JsonIgnore][InverseProperty("User")]
         public virtual List<ChatRoomAccess> RoomAccess { get; set; }
 
+        [JsonIgnore][InverseProperty("Member")]
+        public virtual List<CircleMember> Membership { get; set; }
+
         public DateTime DateCreated
         {
             get; set;