adds comments to new Model_Schedule methods
changes Model_Dao::save() and temporarily makes _create() public
replaces Model_User::_update() with save() on modules/users/main.php
Model_Schedule::get_by_user_day() returns new schedule if empty
modules/users/form.php creates new User when addUser == TRUE
password validation in module/users/main works without id
fixes Model_Dao::_create()
properly implements new CRUD in modules/users/main.php