Introduce CDTMutableDocumentRevision

Created CDTMutableDocumentRevision Class
Modified CDTDatastore to add create, update and delete APIs that use Revisions.
Added basic tests for new APIs
Modified CDTDocumentRevision to add mutablecopy method

Deprecated CDTDocumentBody
Deprecated CDTDocumentRevision method documentAsDictionary
For these tests, you should make a copy of DatastoreCrud and update all the tests to use the new methods, rather than having the few you have below. Then we can be sure things work as they did before, including changing the database appropriately.