Complies with the new MessageType property on API v6

Added the new Channel Types,
Updated RelationshipTypes,
Update all references to PrivateChannels to ONLY select channels that have 1 recipient (DM channels),
Set API.Channel.Type to be non-nullable, as all channels are sent with a type.

Changed GuildEmojiUpdateEvent fields into properties

Added ToString and DebuggerDisplay

Added the namespaces and attribute that are required for this change. Need to get in the habit of doing proper PRs through VS's Git.....

Casting a hex :ok-hand:

Add null-conditional to MessageManager

Update GetGuildMembersAsync, remove paginated GetUsersAsync.