Improve user registration and account update

[SamR1]

• Allow user to update email #106 & Improve user registration #155
  • update username max length (from 12 to 30)
  • display conditions required on registration
  • remove password confirmation
  • add password strength and suggestions
  • add account confirmation step after registration
    • it sends an email in order to confirm registration
    • if a user already exists with a same email, it does not display error (and it does not send a confirmation email)
    • a user with an inactive account cannot log in
  • a user can now change his email. It sends two emails (one to the current address and another one to the new address to confirm it)
  • send an email after password update

• Administration

  • an admin can reset user password (in case the account is locked). It sends an email to the user to change it.
  • an admin can change user email (in case the account is locked). It sends an email to the user new address to confirm it.
  • an admin can activate an account
  • add users search
  • the command to add admin rights also activates the user
  • add admin contact info

• Update documentation