Remove unused import
Wire up links to news items on homepage

Previously, there was no detail view for news items, so the homepage slider
items had non-functional title links.  With the content reorganization
(see f091a9e713331918782d89f1a15c3321aea4f77e), there is now a detail view
for news items, so the links in the homepage slider can now be wired up.

This also fixes a typo in ``NewsItem.get_absolute_url`` where the code
tries to reference ``self.last_updated`` instead of ``self.last_edited``.

Addresses #703