Added support for group channel icons

src/Discord.Net/API/CDN.cs

@@ -8,5 +8,7 @@
             => iconId != null ? $"{DiscordConfig.ClientAPIUrl}guilds/{guildId}/icons/{iconId}.jpg" : null;
         public static string GetGuildSplashUrl(ulong guildId, string splashId)
             => splashId != null ? $"{DiscordConfig.ClientAPIUrl}guilds/{guildId}/splashes/{splashId}.jpg" : null;
+        public static string GetChannelIconUrl(ulong channelId, string iconId)
+            => iconId != null ? $"{DiscordConfig.ClientAPIUrl}channel-icons/{channelId}/{iconId}.jpg" : null;
     }
 }

src/Discord.Net/API/Common/Channel.cs

@@ -35,8 +35,12 @@ namespace Discord.API
         [JsonProperty("user_limit")]
         public Optional<int> UserLimit { get; set; }
 
-        //DMChannel
+        //PrivateChannel
         [JsonProperty("recipients")]
         public Optional<User[]> Recipients { get; set; }
+
+        //GroupChannel
+        [JsonProperty("icon")]
+        public Optional<string> Icon { get; set; }
     }
 }

src/Discord.Net/Entities/Channels/GroupChannel.cs

@@ -16,12 +16,14 @@ namespace Discord
     internal class GroupChannel : SnowflakeEntity, IGroupChannel
     {
         protected ConcurrentDictionary<ulong, IUser> _users;
+        private string _iconId;
         
         public override DiscordClient Discord { get; }
         public string Name { get; private set; }
 
         public IReadOnlyCollection<IUser> Recipients => _users.ToReadOnlyCollection();
         public virtual IReadOnlyCollection<IMessage> CachedMessages => ImmutableArray.Create<IMessage>();
+        public string IconUrl => API.CDN.GetChannelIconUrl(Id, _iconId);
 
         public GroupChannel(DiscordClient discord, ConcurrentDictionary<ulong, IUser> recipients, Model model)
             : base(model.Id)
@@ -37,6 +39,8 @@ namespace Discord
 
             if (model.Name.IsSpecified)
                 Name = model.Name.Value;
+            if (model.Icon.IsSpecified)
+                _iconId = model.Icon.Value;
             
             if (source != UpdateSource.Creation && model.Recipients.IsSpecified)
                 UpdateUsers(model.Recipients.Value, source);