Issue #292 and related to issue #195 . Considered update and create events as different cases. If updated, check all visit_numbers. Added tests accordingly

Issue #195 added tests and changed the post_save function for visit. I didn't saw a problem of concurrency but a problem of saving the visit accordingly. Maybe we need more tests

Issue #276 changed check_nd_number_regex to receive a study and to filter out null or blank nd_numbers in the studySubjects

- 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 signals to Subject and StudySubjet. These signals fire after an instance is saved and check if the subject is excluded, resigned or dead and then call the methods that finish all the appointments and visits. It is safer than doing it on the forms or other parts of the code. Issue #203

Issue #259 : added test to send mail with general appointment and appointment types: test_kit_request_send_mail_with_general_appointment

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

Changed function so the reminder is sorted as well. If no filter is provided then the reminder is all the screening number and it will be sorted with the provided order. Changed tests and the test screening numbers.

Issue #207 . Added custom sorting for screening field in study subject based on the filter introduced in the column. Multivalues are re-sorted