[UPD] Nice page for when a Tiki site is closed

Make a nicer page for when a Tiki site is closed

Here are two prefs to set in the admin panel:

site_closed = "y" site_closed_msg = "Coming soon"

https://doc.tiki.org/Site-Access#Close_site

The default should be nicer.

And it should not say "Maintenance" as it may be something else (like coming soon)