Add missing fileds in DB. Save them in UserModel.php

Adding fields "salt" and "isAdmin" to "simple_login" table in dbSQL.sql
Saving the isAdmin field to DB in function insert() from UsersModel.php
BUGFIX in UsersModel.php, updated dbSQL.sql

Every user in UsersModel.php is now created by default a regular
(non-admin) user.
Updated dbSQL.sql with some user records:
Admin credentials admin:admin
User credentials 111:111 and 222:222