Hide steps for successful scenarios

This will hide the steps of successful scenarios, so that I can see the output of the one failing test, and not have to scroll past a hundred green lines to find it.

I guess this could have been implemented better, but that would mean rewiring the entirety of ecukes-run and ecukes-stats to not rely on side-effects, and instead gather the data and then act on it. This was a way shorter route to the goal. Hope that is satisfactory.

It can be toggled with the var `ecukes-hide-steps-for-successful-scenarios`, but I have not created any command line flags for this.

For some reason that baffles me, I have not been able to get one of the updated tests to actually pass. Instead I get this doozy:

    Test run-scenario condition:
    (ert-test-failed
     ((should
       (equal expected messages))
      :form
      (equal
       ("  Scenario: Simple")
       ("  Scenario: Simple"))
      :value nil :explanation
      (list-elt 0
                (array-elt 0
                           (different-atoms ... ...)))))

To my eyes (and my copy-paste) these are identical.

I also removed the duplicate implementation of `ecukes-print-message` in both ecukes-print.el and test-helper.el.