Add tests for things in utils
Use print_function
Hide directories beginning with _ from the dashboard.

Closes gh-5152
Case insensitive sorting in the dashboard.

Closes gh-5151
Don't attempt locale-aware sorting for now.

On Python 2, locale.strxfrm() can't handle unicode.
Make hidden directories configurable
Fix a couple of static analysis warnings
use on-load event to trigger resizable images

instead of timeout, which could get incorrect size information.

closes #5219
adding visual play button
adding visual interrupt button
add toolbar highlighting on hover
try to have buttons render properly on nbviewer
a less jarring color
initial bootstrap tour

One way to get it to play currently is with a cell like this:

    %%javascript
    $.getScript('/static/notebook/js/tour.js')

provided that you have Bootstrap Tour installed in the components
fix typo for the location of bower.json
add the tour to the page
more work on the tour
starting the tour from the menu works now

JavaScript makes me fond of this phrase:

  When there's nothing left to burn, you have to set yourself on fire.
fix typo in tour.js
allow tour restarting