Sync serialization refactor

[Zetrith]

There's some new stuff to accommodate the fact that Common code has to be independent of Verse and RimWorld but the changes are mostly straightforward.

The moved SyncSerialization provides hook lists for reading and writing but I don't thing we'll be exposing them through the API as they are quite powerful.

Some more details in the commit message.

It's mostly finished but I'm still planning to create a general way of syncing "WithImpl".