(bug 41729) Move section edit links to after the headings

(bug 41729) Move section edit links to after the headings

This requires minor changes in various parts of MediaWiki, and
being extra careful about cached rendered pages' HTML.

Fun fact: editsection links are not made in Parser. They're made in
Linker, in Skin *and* in ParserOutput.

Client-side code and screen-scrapers will have to be adjusted to
handle both cases (old HTML will still be visible on cached page
renders until they are purged); extensions using the DoEditSectionLink
or EditSectionLink hooks might need adjustments as well.

* Linker: Change the HTML of pages to move the link itself from the
  beginning of the heading (before <span class="mw-headline">) to the end
  of the  heading (after the span).
* Skin: Change the class from .editsection to .mw-editsection; we use this
  opportunity to clean up old cruft, and this makes it much easier to
  handle cached renders (by just detecting the old class).
* ParserOutput: Implement a horrible hack to support cached parser
  outputs with the old order of items.
* Ensure everything that should support both classes supports both
  classes (this includes print stylesheets and some scripts).
* Implement styles for the new look for all the skins (did this in
  shared.css; the styles are non-intrusive and can be overridden
  easily, and all of the skins were using the same look before).

Change-Id: I6a6c12a90de3604012420b20c1f520e0ece170ab