Cosmetic changes
Create model User; Add no-brainer tests
Add presence validation tests
Add format validation tests
Add uniqueness tests
Ignore sublime files, once and for all
email is no longer unique, but citizen_number must be
Add password_digest field to Users
fix model, now passing all (uniqueness) tests
add has_secure_password and related tests (end 6.3.4)
update TODO list (end 6)