FB 32224. Removes the _replicator database

This commit removes the _replicator database that was used to control
and monitor replication processes. With this update, the TDReplicator
objects are created directly with TDReplicatorManager. The CDReplicator
objects are conceptually no longer wrappers around _replicator documents,
but instead are wrappers around the TDReplicator objects directly.

The CDTReplicator is initialized with TDReplicatorManager object and
a NSDictionary that specifies the properties of the replication when
created by the CDTReplicatorFactory. There are significant changes to
CDTReplicator.m to make it reflect and monitor the state of the underlying
TDReplicator.

References to the _replicator database are removed from TD_DatabaseManager.
Removes support of "touchdb" protocol for a remote URL from TD_DatabaseManager.
Adds TDReplicatorStartedNotification to TDReplicator.
Adds -createReplicatorWithProperties: and -startReplicator: to
TDReplicatorManager.

By removing the _replicator database, however, there is now no support
to restart replications after the application returns from the background
or is restarted/crashed.
These didn't used to be exposed to the client, so it made sense to zero them out, so that -start doesn't have to if the replication is restarted. Certainly, if this change stays in you need to work out all the times where they need to be reset. This class is resumable, and while our CDT wrapper is not, the class still needs to stand on its own, as that context isn't available here.

Even though we expose this information, I'd therefore suggest we still zero them at this point.