Capture enter when adding additional criteria

Tracker: https://www.pivotaltracker.com/story/show/66409604

Hitting return when adding additional criteria results in the browser submitting the form using the first button. In this case, that is the delete button of the first criteria, which results in the first criteria being deleted because the criteria_action param is not present. This commit adds some javascript to capture carriage returns on the need criteria inputs and submit the form using the correct button.