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 support database structure; SQLite,
  PostgreSQL and SQL Server.
- Fix ignoring `port` config param to specify a custom mysql port.
Lazy Load Schema Tool
Lazy load the schema tool so that if you have not configured your database yet `php artisan` will not crash.
Fixes issues with boolean `--sql` flags.