Minor fixes to announcements, data importer and guides.

# What's New?
 * Fixed a bug where visiting `/guides/new` without logging in would cause a 500 error.
 * Fixed a bug where creating an announcement from RailsAdmin would not work because bool values were interpreted as numeric strings
 * Spruced up ours `seeds.rb` file.
 * Made a tweak to the Crop importer (it's running on staging right now- if all goes well I will run it in production soon)

This one doesn't even make sense. Is hound mad about the name `Fixnum`?