Cleaned up code, added new install.php for web based config configuration

The code and files have been cleaned up a lot. The config can now be
done through install.php, It needs your steam API key to be put in the
top of the install.php file first though.

Simply navigate to yourdomain.com/donate/install.php and sign in through
steam. This will add you as an admin, it uses a very simple mechanism
for this so don't expect much.
install.php will have some defaults and cleverly fill fields with
correct information such as the IPN script URL/Your website and the
PayPal URL. Once you have configured it as needed, click save. It will
ask you to log in again through steam, this is a bug until I get
sessions implemented but will work no problem.