Use ApplicationId for interactions (#2044)

src/Discord.Net.WebSocket/API/Gateway/PartialApplication.cs

@@ -0,0 +1,18 @@
+using Newtonsoft.Json;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Discord.API.Gateway
+{
+    internal class PartialApplication
+    {
+        [JsonProperty("id")]
+        public ulong Id { get; set; }
+
+        [JsonProperty("flags")]
+        public ApplicationFlags Flags { get; set; }
+    }
+}

src/Discord.Net.WebSocket/API/Gateway/ReadyEvent.cs

@@ -28,6 +28,8 @@ namespace Discord.API.Gateway
         public Channel[] PrivateChannels { get; set; }
         [JsonProperty("relationships")]
         public Relationship[] Relationships { get; set; }
+        [JsonProperty("application")]
+        public PartialApplication Application { get; set; }
 
         //Ignored
         /*[JsonProperty("user_settings")]

src/Discord.Net.WebSocket/DiscordSocketClient.cs

@@ -870,6 +870,7 @@ namespace Discord.WebSocket
                                         var activities = _activity.IsSpecified ? ImmutableList.Create(_activity.Value) : null;
                                         currentUser.Presence = new SocketPresence(Status, null, activities);
                                         ApiClient.CurrentUserId = currentUser.Id;
+                                        ApiClient.CurrentApplicationId = data.Application.Id;
                                         Rest.CurrentUser = RestSelfUser.Create(this, data.User);
                                         int unavailableGuilds = 0;
                                         for (int i = 0; i < data.Guilds.Length; i++)