Convert old braket code to use PDO

The ⟨bra|ket⟩-o-matic code base has used a variety of cobbled-together methods for interfacing with the database, the latest being use of PEAR database modules. PHP now offers PDO, which should be used because it is standardized and supported directly by PHP. This will also allow for database swapping if we (I) decide to use a database other than MySQL in the future.