Update Podfile

Remove git link for pod MRDatabaseContentChecker
Add link to coding guidelines
Changes the CDTReplicator -start signature.

-(void)start becomes -(BOOL)start:NSError**

Errors created by TDReplicator objects are propaged from
TDReplicatorManager. They are reported to the Log (via Warn),
but new CDT-level errors are reported to developers using the
CDT API.
Addresses comments in the PR.

Adds synchornization to -startWithError for thread safety.

Adds synchronization to -stop for thread safety.

Mmakes -start a __deprecated method.

Updates tests in ReplicationAcceptance to use the new
-startWithError method.

This commit will be squashed.
Adds tests to ensure that the correct type of TDReplicator is created
by a TDReplicationManager when using the NSDictionary object produced
by the CDT*Replication objects.