Add support for Devise (3.3.x)

Committer note: I prefer to set a pessimistic version contraint on
the Devise dependency. Please note the `Gemfile.lock` MUST be committed
in order to ensure that tests are performed against an up-to-date version
of all dependencies.

See http://guides.rubygems.org/patterns/#pessimistic-version-constraint
Fix dummy app Devise configuration steps

Devise now requires its `config.secret_key` to be set.
Merge branch 'add-support-for-devise-3.3.x'
Bump version number