Extend API for isHidden to make that option more easily user settable

[tigerbot]

I would like to be able to make whether the application is hidden on auto launch user settable, but the current API doesn't make that feasible. There is no way to easily tell if the currently enabled auto-launch is configured to launch hidden, or to change the setting for an AutoLaunch instance.

[adam-lynch]

OK so we need a getter & setter for isHidden. Would you be open to creating a pull-request? 😄