API Spec:
https://docs.google.com/document/d/1LDM8PozLIG2Y0Th7y8NKiEhcED_z-yUXXYEJ29d3wp8
CBL-939 Implement Replicator.start(reset) and deprecate resetCheckpoint()
CBL-787 Replicator.resetCheckpoint does not work as documented