Live sessions - some minor changes

PT story: https://www.pivotaltracker.com/story/show/74032372

Changes:
- added ajax refresh for events show page
- added ajax refresh for hangouts index page
- flattened UI for hangouts index page
- added duration to hangouts details

Refactoring:
- combined attributes into json hash for hangout button
- extracted events show html into partials


consistency is usually a good thing, I agree.  But coffeescript is a lot closer to ruby than javascript and it is usually easier to understand for newcomers than plain js.  Besides, rails makes the use and testing of coffescript absolutely transparent, so I would suggest we allow both in the project.