Add Suport for Read/Write Connections and Ports

- Add compatibility support for 'Database Read/Write Connections' whihc
  was added in Laravel 4.1: http://laravel.com/docs/releases#laravel-4.1
- If db config specifies read/write params a Doctrine
  MasterSlaveConnection will be created instead.
- Add support for specifying the port on which mysql is running on
  hosts.