Initial commit of the feature attendees feature module

This pr is work that reference issues #93 and #111. This has been testing on a fresh cod install base. The only manual changes that need to be done on our end is adding the featured attendees on live once this pr is merged.

Upstream will just need to add the flexslider dependency and do the theming. @willy I added the 'featured attendee' image style as requested so that we are not overriding flexslider's own image style.