Checks are done against the w3.org validator API. Currently we have some
fails. One will be fixed in #2314, others still need to be fixed.

This integration test also reveals some code bugs because texts do not
suppress warnings and deprecation messages.

The code would previously throw a warning when a changelog did not exist
or was empty.

* master:
  fix(search): don't start result position with 2
  refactor(search): clearer data flow
  Change spacing in search meta data to punctuation
  translation update
  translation update
  Fix(search): restore valid heading hierarchy
  fix(search): add position to fulltext results event
  fix(search): ensure consistent html in search results
  Fix invalid HTML in search results
  Fix links with invalid empty target attributes
  Fix buttons with invalid empty name attributes

* recenttypefix:
  Honor type setting for recent changes. fixes #2322

* master: (492 commits)
  Avoid flaky tests by waiting full seconds
  translation update
  translation update
  translation update
  translation update
  Check for null JS object on form field.
  translation update
  Rename _acl_add to _acl_addOrUpdate
  Fix #1115
  translation update
  translation update
  translation update
  Update config.class.php
  translation update
  translation update
  use inline template instead of .dist file to populate users.auth.php
  authpdo: fix _query return type issue per Scrutinizer inspection
  Update lang.php
  Add ugc hint to nofollow
  add UGC hint
  ...

Because we use an online validator

We use the ugc (user generated content) value for no-follow links since #2855
this is not yet supported in the validator.

This patch introduces a list of ignored error messages.