WIP - Rename event and hangout models

## This is work in progress
** The reason why I'm submitting a PR that is not ready to be merged in is because I'm pretty much stuck.**

PT Chore: https://www.pivotaltracker.com/story/show/78137634
- Rename of `Hangout` -> `EventInstance`
- added migration to rename the table and fields containing the word "hangout"
- renamed most of methods to `events_instance_xxx`
- added `gem 'capybara-screenshot'` for debugging purposes

The current status is that __ALL__ specs and jasmine test are passing <font color='green'>__GREEN__ </font>(even the viewspecs for `events/show`). Cucumber is a different story:

   ```
Failing Scenarios:
   cucumber features/hangout.feature:30 # Scenario: Show hangout details
   cucumber features/hangout.feature:47 # Scenario: Show restart hangout
   cucumber features/hangout.feature:56 # Scenario: Restart hangout
   cucumber features/hangout.feature:79 # Scenario: Cancel Edit URL
   cucumber features/hangout.feature:86 # Scenario: Render Join live event link
   cucumber features/hangout.feature:105 # Scenario: Display hangout - basic info
   cucumber features/hangout.feature:138 # Scenario: Display live sessions - extra info
```
Visually the UI is messed up badly (it is as the css and js is not loading but I can't pinpoint where the errors are...).

**Pull down this code, fire up  `$ rails s` and see for yourself. If you know what's up, I'd be happy to hear about it.**

### The UI that I see after the changes in this PR 
![skarmavbild 2014-09-16 kl 22 38 43](https://cloud.githubusercontent.com/assets/5248170/4294723/c35a6918-3de2-11e4-920e-d734995e4400.png)

### The original UI on production
![skarmavbild 2014-09-16 kl 22 49 18](https://cloud.githubusercontent.com/assets/5248170/4294741/f50a7a48-3de2-11e4-81e8-82bba1439704.png)