Capybara 2 upgrade with Capybara-accessible

Features
* Upgrades `capybara` to most current version
* Adds default logo for front end (missing asset causes capybara 2 error)
* Adds `capybara-accessible` gem 

[Capybara-accessible](https://github.com/Casecommons/capybara-accessible) extends Capybara and the Selenium web driver to also use [Google accessibility-developer-tools](https://github.com/GoogleChrome/accessibility-developer-tools/) and test pages for accessibility errors. We fixed one accessibility error and tagged the rest with `inaccessible: true` which skips the accessibility assertions. The hope is that as these tests are updated the flag will be removed and the accessibility errors will be fixed. 

Let us know what you think.

-@ckundo & @tjohn