User sign-in for an existing organization

The user creates an account and claims to be part of one of the already registered organization. This action triggers the sending of an email to the owners of the organisation to confirm (or not) the account creation. Individual details required to create a new account in Gazelle:

• First name,
• Last name,
• Email address,
• Username (between 4 and 16 characters),
• Password (to be entered twice),
• and in that case the organisation the user belongs to.