don’t show maintenance page by default

Following discussion on https://github.com/mattpolito/paratrooper/issues/54, most migrations are quick enough not to need to show the maintenance page. So… don’t bother showing maintenance by default, but allow users to pass in an option if they specifically need to show maintenance.
Merge pull request #62 from bradx3/disable_maintenance_by_default

Don’t show maintenance page by default