Add login feature

- Add application/libraries/uth.php to handle login session
- Add application/controller/user.php to handle login session
- Add application/controller/registration.php to handle registration
feature (not done)
- Add application/views/front_page.php to be first page shown for
logged user
- Add application/views/registration.php for registration page
- Changes in application/config/autoload.php to autoload few libraries
and helpers