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

Fixed problem in commit 47b22f88. Tests didn't fail on my machine. God save continuous integration. Tests passed

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

Issue #239 Removed get_details method and changed extend_context method to use Worker.get_by_user. Enhancement: now the superuser also shows a name in the upper right corner or its username if no full_name is available.

methods modifying structure are replaced with methods that compute arrays that could later on be merged separately