Add Read/Write Connections and sqlite/pgsql/sqlsrv

- Add compatibility support for 'Database Read/Write Connections' which
  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 all other Laravel supported database structure;
  SQLite, PostgreSQL and SQL Server.
- Fix ignoring `port` config param to specify a custom mysql port.