Persistence

Extra work on the persistence branch:
* Made persistence cookie signed and with stuffed some info in it to tie to user
* Validate persistence cookie is for user logging in
* Only drop persistence cookie when users says "remember me on this device"
* Add check box for remember me, off by default (maybe it should default to on during signup?)
* Specs to validate remember me behavior (could use a couple more)
* Fix older spec to check for persistence cookie (not ideal solution, but issue related to cookies and capybara, see this for an example: http://stackoverflow.com/questions/19325960/rails-cucumber-capybara-how-to-set-retrieve-cookies-in-tests)
* Brought branch up-to-date with master (needed my fixed tests from other PR...sorry)