IChannel.IsNsfw will now return false when being used on any channel
that is not an ITextChannel. When being used on an ITextChannel, this
will now account for the API flag, and fall back to the channel name.
(this is gross design, thanks discord)
* Add various property validation in EmbedBuilder
* Embed URI changes
Changes property types for any URLs in Embeds to System.URI.
Adding field name/value null/empty checks.
* including property names in argumentexceptions
* Adds overall embed length check