[ADD] 'auth_generate_password' module to generate randomly user's password

Propose to the community a simple module to:
- block users that can not change them password;
- generate password, and send to the users;

The type of password is defined in two parameters:
- password_size (default : 6);
- password_chars (default : string.ascii_letters + string.digits)

- flake 8 / pylint : OK;
- coverage of the module : ~ 95 %

- [X] change the module icon;
- [X] make this module compatible if password is encryted;
Change it accordingly