simplified feature specs, added more tests and added message for a blank...

... list
If you did remove `@message` and the `@tasks.empty?` check out of the controller and into the view, you can test the rendered view in the controller spec still. See the `render_views` and `expect(response.body).to ...` lines and associated comments in the [Rspec cheatsheet](https://gist.github.com/eliotsykes/5b71277b0813fbc0df56).