don't show the add response button if responses are not allowed.

JIRA: FOR-452
Merge pull request #2446 from edx/rc/2014-02-05

rc/2014-02-05
Make receipt-ids actually generate UUIDs

LMS-2192
Merge pull request #2487 from edx/hotfix/feb-10-2014

Make receipt-ids actually generate UUIDs
Merge remote-tracking branch 'origin/release'