Multiple updates

Updates to gitignore, added migrations folder. Created many to many
relationships between Module model and studentOf, tutorOf etc in order
to solve the use of arrays issue in Person model. Added setting for use
of postgresql and not sqlite3 in settings.
Modified settings, ldap views, and renamed classes

Added LDAP backend settings, renamed LDAP files because of name clashes
in imports, and changed ldap base dn address
Merging changes to develop from feature branches

Re-factored models, and modified tests