First contribution

There are some improvements:
* Easy to configure: Just one file for Database configuration and for
changing the default browser.
* Database abstraction. Now it's easier to change driver (mysql vs
mysqli), with time I'll consider to abstract with PDO or maybe something
lighter.
* Some sql code injections preventions. As none input was escaped in the
original code.
* Better way to check if an input was used. There's a difference between
'($_GET['var'])' and 'isset($_GET['var'])'.
* Other minor changes.