Update to latest version of factory_girl_rails (4.2.1)

  - Update gem
  - Update code to use new syntax required by the latest gem
Restore factories for sample data

Restore the factories that were (wrongly) removed in eea9aea. These
factories were removed because the tests don't use them. However, we
*do* use them to generate sample data. So:

  - Add them back
  - Update them to use the new syntax required by the latest version of
    factory_girl
Update to latest version of tilt (1.4.1)
Declare mongoid_rails_migrations version dependency
Update to latest version of whenever (0.8.3)
Update to latest version of capistrano (2.15.5)
Update to latest version of capybara (2.1.0)

  - Update capybara
  - Update launchy
  - Move affected tests from spec/integration to spec/features as
    recommended by the RSpec docs [1]

[1]: https://github.com/rspec/rspec-rails/blob/1dee0e1cd3/Capybara.md#upgrading-to-capybara-20
Declare fakeweb version dependency
Remove growl

I haven't used growl in months. If I decide to start using it again, we
can always add it back.
Update to latest version of twitter (4.8.1)
Update to latest version of nokogiri (1.6.0)
Update to latest version of rinku (1.7.3)