Add default option for visibleSteps
Add default option for visibleSteps

In production, this is always passed in by the Django view, but it's a good
idea to provide default options in the Backbone view itself for testing the
view isolated from the Django bootstrapping.  It also serves as
documentation of sorts for the view.

denverfoundation/storybase,denverfoundation/storybase,denverfoundation/storybase,denverfoundation/storybase