Do not delete a view when its associated group is deleted (#11)

This PR does a few things, mainly changes the `belongs_to :group, :dependent => :destroy` to `:nullify` instead so users can delete a group without losing all the views associated to that group.

Other changes include:
- Stop using really old versions of test-specific gems
- Remove a file that was causing Ruby malloc errors when running specs
- Shuffle an `include` in `spec_helper.rb`
- Refactor the `View` feature spec