Implement replicate command

This is a direct replacemnet of the stream command. It wires the doozerd given via `-uri` directly to the doozerd passed to the replicate command and applies mutations in a streaming manner. Preceeded by an initial sync much like the journal command is doing to dump the initial state.

This is the direct replacement of [doozerd-replicate](https://github.com/soundcloud/doozerd-replicate) repo which is not necessary given all shared code already exists in this repo and providing it as another command makes for better cohesion.
***
@soundcloud/iss