SQL injection prevention

Hi,

This should fix the SQL injection issue. I was going to use the generic `PDO::quote` (http://www.php.net/manual/en/pdo.quote.php) but after looking closely at the structure of the completely insane `select` function in `DatabaseRequest.class.php` and how it is used throughout the project (Supplying filters as Arrays in various formats) i am convinced this is not a viable option .

I tested this commit on our local robinhood installation, it is working.