add nsurlcache to appdelegate
trying to force response to cache without cache-control header

headers (via curl -i http://www.citibikenyc.com/stations/json)
----------
HTTP/1.1 200 OK
Date: Tue, 19 Aug 2014 03:07:30 GMT
Server: Apache/2.2.15 (Red Hat)
X-Powered-By: PHP/5.4.30
x-version: 1.0
Last-Modified: Tue, 19 Aug 2014 03:07:01 GMT
Vary: Accept-Encoding,User-Agent
Connection: close
Transfer-Encoding: chunked
Content-Type: application/json
----------