Have WT RTT rollback keep correct counts

SERVER-33488 describes how counts in RTT WT can diverge with reality across restarts. This ticket is for correcting counts across rollbacks. The proposal:

Have the rollback op observer track the inserts/deletes being rolled back for each collection/UUID. Use this information to adjust counts.

I expect this correction to not be crash-resistant so long as replication truncates the oplog before recovering forward from the stable point to the common point. In general, WT already has problems keeping correct counts across crashes.