Networking improvements

Over the past few weeks, I was mostly focused on networking. Me and the author of bevybundlication have decided to collaborate. The plan is to abstract his crate over bevyreplicon and ensure that rollback crates could be used together with it nicely.
After a lot of discussions, we came up with a very elegant API and today I finally finished implementing it! A few follow-ups will be needed, but everything should be ready soon :)

@projectharmonia

bevy #projectharmonia