Fixes #148 - JSON response to pressing back button

- Creates html and json format response in organizations controller for
handling regular and AJAX page loads.
- Adds private method to organization controller to handle returning
partials in JSON and HTML requests.
- Sets caching to false and Accept header to application/json for AJAX
requests using jQuery.
Adds AJAX called flag to prevent redundant refresh of AJAX request

To handle the browser back button, the AJAX script needs to listen for
when the history's popstate is fired, and respond when the back button
is clicked on a page that uses AJAX. This led to a redundant call to
the AJAX request when the page first loaded. This commit adds a flag
that is set to false initially.
Merge pull request #188 from codeforamerica/148-fix-history

Fixes #148 - JSON response to pressing back button