adds test for params[:time_limit] in questionnaire create
* moves link to questionnaire editor to nav bar, removes temp link from home page
* changes DEBUG label in div.debug to DEMO
* bug fix: participant entries couldn't be deleted from table in questionnaire editor because of a call to undefined $this -> changed to $(this)
* bug fix: calling event.stopPropagation() on undefined event var when moving between input fields with input_keydown. added ... if event
adds admin authentication to QuestionnairesController
adds one-to-to relationship to questionnaires and admins
adds admin_id to questionnaire creation
adds fields for teacher feedback to result table (not sending mails yet)
bug fix: only one answer_sheet per student, overwritten for every time a test is completed. Replaced AnswerSheet.find_by_student_id with AnswerSheet.find_by_student_id_and_questionnaire_id in AnswerSheet#prepare
bug fix: correct order when cycling through question blocks via nav buttons in test (cf. same bug in questionnaire editor; not entirely sure if actually fixed!)
changes evaluation of multiple-choice question: 1 credit per question, if and only if exactly the right options have been chosen (not tested thoroughly)
adds rudimentary support for youtube links in questions (not fit for actual deployment)