Better header display

Change-Id: I4aa4f1d30b22b863df9fc46b78fac7442ff5def7
Feedback link on article pages

* Add API endpoint to fetch amount of entries for a given page/filter
* Code for above functionality was in use on special page already; moved
  that code to utils so both can access this and avoid code duplication
* add Javascript ajax call to fetch the amount of feedback and display a
  link on article page
* Update talk-page link to also only display if there is feedback

Bug: 42057
Change-Id: I03c815d8257aaa590ef639387c360d8356cd0d96

Conflicts:
	modules/ext.articleFeedbackv5/ext.articleFeedbackv5.css
	modules/ext.articleFeedbackv5/ext.articleFeedbackv5.talk.js
Improve opt-in/-out

Change-Id: I511ce6250b87694e0c010ef38a1e7cb950266e63
Further improve stuff

Change-Id: Ida12c404cc9c913ff086f398d8c04601a4c4d1f5