This commit mostly addresses the organization of the CDT*Replication classes.
In particular, these classes more resemble the similar implementations in the Andriod library.

* -source: and -target: methods were moved to CDTPush/PullReplication explicitly. There are
no baseclass methods with these names.

* decomposed the NSURL into accessible components. A NSURL* variable no longer exists
within the classes, but is rather computed on the fly. (This may change now that
I've heard about NSURLComponents -- but this is iOS 7 and OS X 9 only, so we may want
to think about it.)

* NSError** was added to the signature for the -dictionaryForReplicatorDocument methods.

* CDTReplicationTests was added to verify the behavior of the CDT*Replication classes.

This commit, along with the previous two, will be squashed to a single commit
when merged into master.