principal_event is null #3377

for ppg fu event.

Added ppg fu to list of principal events.

Closes #3377
Merge branch '1.3.8.patch'
bump version to 1.3.8
Merge branch '1.3.8.patch'
Added events association #3389

to contact through the contact_links association
Determine the consent event #3389

associated with the ParticipantConsent