Add mute role support & fix /unmute (#109)

- Added support for `MuteRole`, now if you add any role to this setting,
then try to mute a member, all his roles will be removed except for the
one you set in this setting.
- Fixed `/unmute`, that tried to set target's display name to unmute
reason.

---------

Signed-off-by: Macintosh II <mctaylxrs@outlook.com>

src/Responders/GuildMemberRolesUpdatedResponder.cs

@@ -23,7 +23,11 @@ public class GuildMemberUpdateResponder : IResponder<IGuildMemberUpdate>
     public async Task<Result> RespondAsync(IGuildMemberUpdate gatewayEvent, CancellationToken ct = default)
     {
         var memberData = await _guildData.GetMemberData(gatewayEvent.GuildID, gatewayEvent.User.ID, ct);
-        memberData.Roles = gatewayEvent.Roles.ToList().ConvertAll(r => r.Value);
+        if (memberData.MutedUntil is null)
+        {
+            memberData.Roles = gatewayEvent.Roles.ToList().ConvertAll(r => r.Value);
+        }
+
         return Result.FromSuccess();
     }
 }