refactor: cache own user ID in IDiscordCache

- remove Cluster.User
- remove Cluster.Application (it was only being used as an alternative to Cluster.User for some reason)
- move Bot.PermissionsIn to DiscordCacheExtensions

PluralKit.Bot/Commands/Checks.cs

@@ -87,7 +87,7 @@ namespace PluralKit.Bot
             var missingEmojiPermissions = false;
             foreach (var channel in await _rest.GetGuildChannels(guild.Id))
             {
-                var botPermissions = await _bot.PermissionsIn(channel.Id);
+                var botPermissions = await _cache.PermissionsIn(channel.Id);
                 var webhookPermissions = await _cache.EveryonePermissions(channel);
                 var userPermissions = PermissionExtensions.PermissionsFor(guild, channel, ctx.Author.Id, senderGuildUser);
 
@@ -176,7 +176,7 @@ namespace PluralKit.Bot
             if (!await ctx.CheckPermissionsInGuildChannel(channel, PermissionSet.ViewChannel))
                 throw new PKError(error);
 
-            var botPermissions = await _bot.PermissionsIn(channel.Id);
+            var botPermissions = await _cache.PermissionsIn(channel.Id);
             var webhookPermissions = await _cache.EveryonePermissions(channel);
 
             // We use a bitfield so we can set individual permission bits

PluralKit.Bot/Commands/Lists/ContextListExt.cs

@@ -61,7 +61,7 @@ namespace PluralKit.Bot
                 p.IncludeLastSwitch = true;
             if (ctx.MatchFlag("with-last-message", "with-last-proxy", "wlm", "wlp"))
                 throw new PKError("Sorting by last message is temporarily disabled due to database issues, sorry.");
-                // p.IncludeLastMessage = true;
+            // p.IncludeLastMessage = true;
             if (ctx.MatchFlag("with-message-count", "wmc"))
                 p.IncludeMessageCount = true;
             if (ctx.MatchFlag("with-created", "wc"))

PluralKit.Bot/Commands/Misc.cs

@@ -59,7 +59,7 @@ namespace PluralKit.Bot
 
         public async Task Invite(Context ctx)
         {
-            var clientId = _botConfig.ClientId ?? _cluster.Application?.Id;
+            var clientId = _botConfig.ClientId ?? await _cache.GetOwnUser();
 
             var permissions =
                 PermissionSet.AddReactions |

PluralKit.Bot/Commands/ServerConfig.cs

@@ -59,7 +59,7 @@ namespace PluralKit.Bot
             if (channel.Type != Channel.ChannelType.GuildText)
                 throw new PKError("PluralKit cannot log messages to this type of channel.");
 
-            var perms = await _bot.PermissionsIn(channel.Id);
+            var perms = await _cache.PermissionsIn(channel.Id);
             if (!perms.HasFlag(PermissionSet.SendMessages))
                 throw new PKError("PluralKit is missing **Send Messages** permissions in the new log channel.");
             if (!perms.HasFlag(PermissionSet.EmbedLinks))