------
- minor fixes to templates (edc-dashboard, edc-subject-dashboard,
edc-navbar)
- add system check against SubjectScheduleHistory and the OnSchedule
model (edc-visit-schedule, edc-appconfig)
- management command to delete invalid onschedule instances
(edc-visit-schedule)
- fix issue where form runner fails on PRN forms that do not
have visit schedule fields (edc-form-runners)