fixes #1728 adds ordinal numbering

@wescott 

Two parts of the logic:
* The rendering to user looks for an `<h3 class="questionNumber">` inside each `<div class="question">`.  If that doesn't exist, then it adds an ordinal number.  If such a div does exist, it's left alone. If there's only one question, the code does nothing.
* The import to html looks for a `do-not-autonumber` attribute inside the `<problemset>` tag.  If it exists, or if there's only one question, the import will populate blank numbers (`<h3 class="questionNumber"></h3>`).  Otherwise it fills the content of the `<h3>` with the calculated ordinal (Question 1).