[kronolith] Guest Services Calendar

[mbydalek at zivix.com]

Is there a way to set a static calendar for Guests?  What I mean by this is that
I setup a calendar called "Public Calendar" that I want to use for guest to
see.  The problem comes into play due to the drop-down being shown to "Show
Calendar:"  If someone unselects the guest calendar, Horde throws errors from
kronolith/lib/base.php on line 100.

To prevent this, it would be nice that all guests default to show all calendars
- that are within their permissions - basically any calendar that has Guest
marked as Show.

This also brings up a point that any new calendar has "Guest -> Show" checked in
permissions, which personally seems not right.

Thanks,
Mike