Add owner/administrator check to RequirePermissionAttribute

A 'Fuzzy' property has been introduced for people who want
the old behavior of ignoring owner/administrator checks,
which can be used something like this:

[RequirePermission(permission, Fuzzy = false)]

src/Discord.Net.Commands/Attributes/Preconditions/RequirePermissionAttribute.cs

@@ -8,22 +8,34 @@ namespace Discord.Commands
     {
         public GuildPermission? GuildPermission { get; }
         public ChannelPermission? ChannelPermission { get; }
+        public bool Fuzzy { get; set; } // public for `RequirePermission(permission, Fuzzy = false)`
 
         public RequirePermissionAttribute(GuildPermission permission)
         {
             GuildPermission = permission;
             ChannelPermission = null;
+            Fuzzy = true;
         }
         public RequirePermissionAttribute(ChannelPermission permission)
         {
             ChannelPermission = permission;
             GuildPermission = null;
+            Fuzzy = true;
         }
         
         public override Task<PreconditionResult> CheckPermissions(IMessage context, Command executingCommand, object moduleInstance)
         {
             var guildUser = context.Author as IGuildUser;
 
+            if (Fuzzy)
+            {
+                if (guildUser.Id == guildUser.Guild.OwnerId)
+                    return Task.FromResult(PreconditionResult.FromSuccess());
+
+                if (guildUser.GuildPermissions.Administrator)
+                    return Task.FromResult(PreconditionResult.FromSuccess());
+            }
+
             if (GuildPermission.HasValue)
             {
                 if (guildUser == null)