fix invalid HTML.

I used http://html5.validator.nu/ to find invalid. We still have
2 kinds of invalid one:

    a. <col width="30px"> in paticipants page
    b. rel="tooltip" (see https://github.com/twitter/bootstrap/issues/6284)
Merge pull request #479 from eller86/451-fix-invalid-html

close #451: Fix invalid HTML