Upgrade less.js to 1.4.1

This was an attempt to see if the newer version of the library has
better support for refreshing the uncompiled less files when in
development mode.
Update styling for the "Activity Guides" page

Initially, only show the title and toggle additional content with
JavaScript.  To deal with variable-height elements, use the
Masonry JavaScript.

To add the JavaScript, use a custom CMS template,
``activity_guides.html``.

Rename LESS stylesheet from ``activity.less`` to
``activity_guides.less``

Addresses #864
Update changelog to reflect activity guide styling

Addresses #864
MIT License