Revise implementation of orphaned object deletion to avoid inappropriately deleting when the `modificationKey` attribute optimization is in use. refs #1328
Test for #1328

Also added Meeting and Party to Data Model for testing Dynamic Mapping with Core
Data models.

Signed-off-by: Blake Watters <blakewatters@gmail.com>
Fix issue with relationship traversal when gathering objects for orphan comparison
Rework cancellation behaviors so that the failure block and error are invoked.

* Add new error code for cancelled operations
* Ensure the failure block is called when cancelled