27480 replication test

This PR adds a ReplicationAcceptance project which is designed to be run standalone to make sure replication is working. The project is completely standalone, in that it isn't in the CDTDatastore workspace, as I plan to run it nightly.

If you want to test locally, change the `n_docs` variable in `ReplicationAcceptance.m` to perhaps 10k rather than 100k. See `README.md` for how to run the test.

See the comments in `ReplicationAcceptance.m` for a description of each test.

The tests only run against a local CouchDB right now; I need to work out the best way to securely get Cloudant credentials set up. Help with this appreciated.