Fixed survey_response/read to allow time-zones.

The 'start_date' and 'end_date' parameters were not allowing a user to send a W3C ISO-8601 timestamp with a time and time-zone. This has been corrected.
Fixed a bug when uploading timestamp prompts.

Timestamp prompts were uploading timezones but they were not properly being saved. They are now.
Merge branch 'master' of github.com:cens/ohmageServer into ohmage-2.15