Fix GuildPermission Modify, Add Missing Permission to AllowAll

[Chris-Johnston]

I was told (by The Noodle Mummy#0339 and Spoopy Ghost Dog#5440) of an issue with GuildPermissions#Modify producing incorrect results. My discord handle is ChrisJ#8703.

This code snippet:

[Command("testing")]
public async Task testing(SocketRole role)
{
   await role.ModifyAsync(rp => rp.Permissions = Optional.Create(role.Permissions.Modify(changeNickname: false, manageNicknames: false)));
}

Would produce this result (as seen in Audit Logs):

Now appears to be working correctly:

Problem was caused by a parameter (manageRoles) out of order in GuildPermissions: https://github.com/RogueException/Discord.Net/blob/dev/src/Discord.Net.Core/Entities/Permissions/GuildPermissions.cs#L135

In addition, I was also told that the following snippet:

SocketGuildChannel c = arg.GetTextChannel(313504029437329410);
OverwritePermissions perms = OverwritePermissions.AllowAll(c);
await c.AddPermissionOverwriteAsync(arg.GetUser(270390842923941888), perms);

would execute without problem, but was missing the WebHook permission. This is fixed in ChannelPermissions, and appears to be working properly now.