exposing getters and setters on replicator classes

This change is mainly for parity with the iOS version.  New methods are:

* CBLPusher.isCreateTarget()
* CBLReplicator.getFilterName()
* CBLReplicator.getFilterParams()
* CBLReplicator.isContinuous()
* CBLReplicator.setContinuous()

Calling setContinuous when replication is running has no effect.  Since these are all simple getters and setters, I didn't add unit tests for them.