ProgressBar() module to display output to a console or iPython Re: issue#2658

Modified ProgressBar() module to display output to a console or iPython notebook, depending on additional 'interactive' kwarg.

Description of the issue and possible fix here: http://nbviewer.ipython.org/gist/astrocaribe/398d04434430c3f44617

@embray Included your above suggestions in latest commit 74b2f33. Will need help figuring out how to rebase @keflavich's #2793 into my branch. Also need to discuss your above suggestion of creating a separate utility for formatting progress bar output (if I understand your above point correctly).