If pattern matches without a labelled date group, skip the interval test.
Support validation of enrollment.

* Synthesize validation events from Sqoop dumps of
  student_courseenrollment.

* Compare validation events with enroll/unenroll events.
  Includes unit tests.
Define "generate-before" option.

When true, generate events from before the defined interval.  Default is false.

Also patch handling of is_active from synthetic enrollment validation events,
to deal with string input.
Change validation event "is_active" from string to boolean.
Give Synthetic events timestamps that are a microsecond different from the source events.
Add CourseEnrollmentValidationPerDateTask to group synthetic events by date.