Add "unanswered" tab to view tags page

[snytkine]

Add sorting tab "unanswered" to be able to sort tags by 'unanswered'
Then in controller Viewqtags add sorting by 'unanswered' and then
in Cache.php uncomment the line that has this:
{WEB_ROOT}/{viewqtags}/{unanswered}
in order to be able to add link "view all unanswered tags"