Live sessions - some minor changes

PT story: https://www.pivotaltracker.com/story/show/74032372
Demo: http://yaro.herokuapp.com/hangouts

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