Message.lvclass an interface

[CaseyZS]

Is your feature request related to a problem? Please describe.
Not a problem really, but there's no reason that Message.lvclass can't be an interface now. It could open up some neat possibilities for the future of AF.

Describe the solution you'd like
Make Message.lvclass an interface instead of a class. Project Providers that use Message.lvclass (e.g. Message Maker) would also need to be validated against this change.

Describe alternatives you've considered
Derrick (Illuminated G) already has a VIP out that does this but it could be integrated into native AF.

Additional context
N/A

[svelderrainruiz]

sandbox branch for @niACS users/asmith/message-class-interface has been created at his request, since this is going to be a long standing experiment.