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

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

during save study is automatically injected into model

during save study is automatically injected into model

address, city, country, data_born, default_written_communication_language, email, first_name, languages, last_name, phone_number, phone_number_2, phone_number_3, postal_code removed from study_subject (all this information is stored in subject)

the code is fixed so unit test passes