Fix question page titles when only one question

There should only be a question page title if there are more headings
than questions, which is the same logic as in question.

This was causing a question page title, the same as the first (and
only) question, to appear within previous answers.
Only parse govpseak if there is something to parse

Passing an empty string  to GovspeakPresenter will return n, which is
A) unexpected
B) was causing problems when comparing the output of the same question
   in smartdown and in original smart answers.

If there's no govspeak input we should return nil
Merge pull request #62 from alphagov/whitespace-and-bugfixes

PreviousQuestionPage title and whitespace bugfixes