Move RpcCategoryChannel into the correct project

experiment/Discord.Net.Rpc/Entities/Channels/RpcCategoryChannel.cs

@@ -0,0 +1,36 @@
+using Discord.Rest;
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+using System.Threading.Tasks;
+using Model = Discord.API.Rpc.Channel;
+
+namespace Discord.Rpc
+{
+    [DebuggerDisplay(@"{DebuggerDisplay,nq}")]
+    public class RpcCategoryChannel : RpcGuildChannel, ICategoryChannel
+    {
+        public IReadOnlyCollection<RpcMessage> CachedMessages { get; private set; }
+
+        public string Mention => MentionUtils.MentionChannel(Id);
+
+        internal RpcCategoryChannel(DiscordRpcClient discord, ulong id, ulong guildId)
+            : base(discord, id, guildId)
+        {
+        }
+        internal new static RpcCategoryChannel Create(DiscordRpcClient discord, Model model)
+        {
+            var entity = new RpcCategoryChannel(discord, model.Id, model.GuildId.Value);
+            entity.Update(model);
+            return entity;
+        }
+        internal override void Update(Model model)
+        {
+            base.Update(model);
+            CachedMessages = model.Messages.Select(x => RpcMessage.Create(Discord, Id, x)).ToImmutableArray();
+        }
+    }
+}