Submit KPI data when the dialog closes either in the interaction_iframe OR in the internal_api.

Only generate GUIDs for a KPI blob whenever needed:

* When the dialog is orphaned AND
* A staging event occurs without a confirmation event.
Instead of sending a GUID to associate two KPI blobs, set "staging_continuation" in the event stream.
Merge pull request #3495 from shane-tomlinson/issue_3306_kpi_this_session

Submit KPI data when the dialog closes either in the interaction_iframe OR in the internal_api.