- Add field default_delta_time_for_control_follow_up to study
- Add field default_delta_time_for_follow_up_units to study
- Add field default_delta_time_for_patient_follow_up to study
- Alter field default_visit_duration_in_months on study
- Alter field default_voucher_expiration_in_months on study

added checks for forms
added check function in Study and StudySubject to avoid repeating a regex inline
removed previous checks in which the regex was rewritten
now the used regex is the one defined in the given study
added tests and migrations
changed functions in tests/functions to adapt the tests

there is singleton study columns object created in db to reflect current state of the project (single study per smasch instance)