Add new question type file

[srobotta]

Hi Mike,

this is a new pull request for the new file type question and replaces #559
The original work on the file type has been done by Laurent David (https://github.com/laurentdavid). He introduced this question/response type and also created #471
Luca Bösch added behat tests for the new file type.
I finally fixed a few issues from the original work from Laurent:

• deletion of left over data when a response or the whole questionnare is deleted.
• possibility to have multiple file type questions in one questionnaire.

I have taken your latest MOODLE_401_STABLE branch from the plugin and our codebase from BFH where this is already included and created this pull request that just contains the file type.

[mchurchward]

Thank you for all the effort you have put into this. I will review this happily.

[srobotta]

Just rebased to the latest MOODLE_401_STABLE branch.

[mchurchward]

I know this is old, but I was just testing it on MOODLE_404_STABLE and it didn't work.
I had a number of odd issues.

1. If I saved a response instead of submitting, when I went to resume the questionnaire, my file was not in the file question.
2. If I then uploaded it again, and submitted, I received the error "Undefined property: stdClass::$itemid" from the responsetype/file class when it went to delete the old response on line 136.
3. When I did it again, and submitted the first time, it worked. But the response page showed me a question response to rate question from another questionnaire.
4. I believe this will need backup and restore support code added?