Improve validity of html

Try and put all questions/sections under an <li>
Don’t add `.q_hidden` class to questions hidden as a group.

When a question is part of a group it’s hidden by the groups css dependency and doesn’t need a class to hide itself as it then doesn’t show up when the group is shown.
Don’t need the extra `<ol>` that `inputs` inserts.
Name what this check does

and put in in the question model instead of the view
Show urls as explained on initial load of questionnaire
Merge pull request #975 from theodi/feature-valid-html-form

Improve form html generation