Add help link for 8 more special pages

Add help link for 8 more special pages

* Links can now be customised on-wiki via system message:
  e928d5bdd0fbc63a951ca373aaf68bb1e6bf715c
* Most help pages chosen here are good for any MediaWiki install
  and have been imported on MediaWiki.org. Their license has been
  noted in the appropriate template, only future contributions
  will be in public domain (CC-0) unless we reach old authors.
  An update/discussion was opened at the project talk:
  https://www.mediawiki.org/wiki/Project_talk:PD_help
* The 6 pages on MediaWiki.org have been marked for translation;
  import of previous translations is ongoing. 2 pages are left on Meta
  because importing translatable pages with all translation units may
  be overkill.

Bug: T45591
Change-Id: I5dd91a0b7233556f2da06b65205fee72ea65a55f