Fix bug 931156: ensure breadcrumbs update during page move.

This does some significant refactoring, but not really changing, of
the page-moving code, breaking up the monolithic _move_tree() into
multiple shorter methods which each handle a smaller piece of the
puzzle (for easier debugging/editing).

The only genuine change is that Document.save() no longer attempts to
create redirects when a slug is edited; the redirect logic is now
called during page move, and the move() method, which existed only to
do that, is removed. This is considered safe because the only way to
edit a slug outside of page-move is through the Django admin, and this
commit also removes that ability, along with any tests that tried to
exercise the automatic redirects on non-move slug edits.
Updates to layout for small desktop asked for by JYP.  Non-breaking main nav at small width and adding wrapping crumbs
fix bug 918233 - Reduce list font sizes
Minor manual installation documentation update.

You cannot push to git://github.com/<your_username>/kuma.git.
`your_account` is renamed to `your_username` for consistency with
installation-vagrant.rst
fix bug 933708 - Enforce deviice-width on mobiles
Multiple a11y updates for search accessibility. Thanks to icaaq
Stop loading CKEditor on basic document pages
Merge pull request #1570 from darkwing/small-desktop-update

Updates to layout for small desktop asked for by JYP.  Non-breaking main...
Merge pull request #1571 from darkwing/titles-918233

fix bug 918233 - Reduce list font sizes
Merge pull request #1572 from nhenezi/minor-doc-update

Minor manual installation documentation update.
Merge pull request #1574 from darkwing/force-media-width-933708

fix bug 933708 - Enforce deviice-width on mobiles
Merge pull request #1575 from darkwing/a11y-search-enhancements

Multiple a11y updates for search accessibility. Thanks to icaaq
Merge pull request #1576 from darkwing/remove-ckeditor-all-pages

Stop loading CKEditor on basic document pages
Merge pull request #1562 from ubernostrum/page-move-parent

Fix bug 931156: ensure breadcrumbs update during page move.