Add top help link to MediaWiki.org in several pages via indicator

All the chosen targets are translatable public domain help pages
on MediaWiki.org. Mostly special pages and actions for privileged
users for now.

Adapted from the Translate extension, credit to Niklas Laxström
(TranslateUtils::addSpecialHelpLink).

Depends on 6f5b29ff4e6fdf21b5a8cacaf10d6aceaee26a7d, whose commit
message has a typo addIndicator() instead of setIndicator().

Bug: T45591
Change-Id: I2934b1708a0d207dcf3d940264f140613646f203