Exit and display error msg when no config.php file is found

Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
install: Don't pass class name when inserting user

Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Add SITE_PATH when looking for existing config.php

Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>