Add Creator property to (Guild?)Emote

[Joe4evr]

Discord's API returns the user who created an emote as part of the emote payload. We should give users the ability to access that if possible.

Proposed addition:

public partial class GuildEmote
{
    public Optional<IUser> Creator { get; }
}

Update: Adjust to feedback.

[FiniteReality]

This would probably only work on GuildEmote as Emote does not have the information required to have a Creator property, as it's mainly created using Emote.Parse("<:name:id>").

I see no problem with adding it to GuildEmote, however.

[foxbot]

Resolved via 92bf836