fixed "prosegui" alignment

kinda hackish, but it should work
changed css names
prettified questions.css
fixed completed page

- to access it, has to completed the survey and be logged in
implemented a common lib & extra changes

- common.php: should contain functions to clean other php files
- verify.php, completed.php: now using common.php

extras:
- settings.php: deleted old settings
- reset.php: must not be present in production code
fixed logout code
changed logout icon

it wasn't grey
commented verify.php
questions.php & changed the way common.php works

- created functions for single/multiple result queries
- created a function to get a singleton-like db connection
- questions.php now uses common.php