New page title should not be pluralized

Created by: dvanderbeek

This: https://github.com/thoughtbot/administrate/blob/2c54226aeaebc1ac5316ccd22e87d3080e3608ed/app/views/administrate/application/new.html.erb#L21

Should probably use the same logic as this: https://github.com/thoughtbot/administrate/blob/2c54226aeaebc1ac5316ccd22e87d3080e3608ed/app/views/administrate/application/index.html.erb#L47