Added method docstring and removed unnecessary comment from inside
_clean_inactive_users is now a static method to be easily used for testing
Insert new method that tests the removal of users whose activation time is expired
Removed control of existing password from create_user function.
Now the control is made in the create user POST request.
Fixed indentation
Added test method for an user creation (POST request) without password
Delete unnecessary control of existing password in activate_user function.
Activate_user is called with a PUT request which doesn't require a password
Fixed create_user function call: it must have 3 parameters
Fixed encrypted password .
Activate_user function was encrypting an already encrypted password which was wrong.
User's password was already encrypted once with the create_user function.
Added new test for a PUT request activation user with no password