Creates individual threads for each TDReplicator.

This commit moves all of the threading code from TDReplicatorManager
to TDReplicator so that each TDReplicator executes on its own thread.

No new tests are yet written to monitor multiple replications at
once.
Fixes security issue where passwords were being sent to the log.
Adds test for multithreaded replication.

Two pull replications are executed simultaneously, pulling
from the same remote database to two different local databases.
A delegate captures updates from the replicators and determines
if the replicators were operating simultaneously.