Refactoring

Moved migration publishing functions out of MigrateCommand and into a MigrationPublisher
class.  Updated ZipCodeServiceProvider.

Removed ./src/seeds

Updated ./src/add_wgs84distance_function.php to use connection from config file. This
will still cause problems if the connection changes between running the migration
and rolling them migration back.

Changed source argument to an option in commands zipcode:migrate and zipcode:seed.