R1:8669c3c0d226

When updating a workboard with "R", send the client visible set with version numbers

Summary:
Depends on D20652. Ref T4900. When the user presses "R", send a list of cards currently visible on the client and their version numbers.

On the server:

- Compare the client verisons to the server versions so we can skip updates for objects which have not changed. (For now, the client version is always "1" and the server version is always "2", so this doesn't do anything meaningful, and every card is always…