Official answer (WIP)

Verified officials can submit answers to questions asked of them and those answers are shown on the question page.

### Added features:
* Created Answer model and spec
* Created AnswersController to handle create method, verifying answer can only come from the correct verified official
* Rendering answer on question #show
* Created simple answer submission form when official is already signed in
* Hiding answer submission form when question has been answered

### Todo:
* spec for proper answered boolean behavior when question submitted
* feature spec for submitting and rendering answers

### Work in progress (WIP)
@walter & @davidmooreppf this pull request is still a WIP, but wanted to push this up so you could take a look at our progress so far. A few notes:

* Noticed there was no model for storing answers, so we stubbed one out. @evz and I weren't sure if we wanted to support more than one answer, so we hedged on the model supporting it. 
* What should we do with the Sign On buttons once a question has been answered? Keep it active?
* What if an official answers a question _before_ a it reaches the signature threshold? Do we have a story for this?
* Now that we're showing answers, we need some styles to indicate a question has been answered on the question #index and #show views.