Disable or fix nonfunctional saved searches [MJ-931]

There are now four separate email methods on SavedSearch. Perhaps it's time to condense them.

All tests pass. I would like to see if Jenkins tests pass before merging, however, since it doesn't use the Celery test runner.
The wording for this is a little strange. @fezick - would saying `Your search, "{{ saved_search.label }}", is no longer valid and has been disabled.` or something similar work? I just don't think the average user would know what URL validation is.