Expose Sponge provided packet protocol

[gabizou]

Sponge uses a custom payload packet with the channel sponge to perform various things. Currently, it's limited (in both 1.8.9 and 1.9.x) to request and receive block/entity ownership information. This does perform a server side permission check, but custom clients would be able to request this sort of information without requiring say SpongeForge on the client.

I'm not 100% whether we should bother at the current time, but @bloodmc and @Zidane, I've had ideas to possibly expand on our custom messages to provide some more information in the future, more in the future where a toggle for the server notifying clients of notifier/ownership changes as they happen on the server (something @Mumfrey and myself though up a few weeks back to provide a visual identification system on clients with color coding and the sorts).

Nonetheless, these messages and protocols should be documented, in my opinion, on the best documentation collection that Sponge provides (the SpongeDocs of course!).