No HasID instances for FullContext and LightContext?

[MorrowM]

Is there a reason FullContext and LightContext don't have HasID Channel/Message/User instances? It'd be quite nice for e.g. invoke $ CreateMessage ctx $ def ... rather than having to use ctx ^. #channel all the time.
If not I'd be glad to make a PR.

[simmsb]

I can't remember a reason for not having HasID on Context if there was a reason originally, so go ahead.