Remove "New Calendar" page's .ics file importer button footgun
A file imported as a "new calendar" would make it dependent on the file. This feature was confusing everybody and is downright dangerous.
This does not prevent anyone from creating normal calendars, and importing events from .ics files into them.
Not only did this complexify the UI, it was also a footgun.
Fixes #390
Edited by Jeff Fortin