Merge remote-tracking branch 'origin/bugfix/8037-install-localized-wikipedia-searchplugins' into testing

Merge remote-tracking branch 'origin/bugfix/8036-workaround-for-localized-searchplugins' into testing

E.g. if our locale is pt, which doesn't have localized search plugins,
we'll use one of pt-PT and pt-BR.

Merge branch 'bugfix/8122-better-browser-localization' into bugfix/8036-workaround-for-localized-searchplugins

Conflicts:
	config/chroot_local-includes/usr/local/bin/tor-browser

That is for the various browsers and Tor Launcher. This will make it
possible to drop the browser localization code from Tails Greeter's
PostLogin script, where that really doesn't belong.

Also, this new code is an improvement in that it will pick a "similar"
locale if the specific one we look for isn't available. E.g. with
pt-BR we will get pt, and the Firefox is smart enough to use the pt-PT
langpack.

... than the old one we used prior to the TBB migration, so our
branding addons wouldn't set it as the default for en-US (and locales
without a localized Startpage plugin, which falls back to en-US).

Previously we got them from the iceweasel-l10n-* packages, but we do
not install them since the TBB migration.

This shift was forgotten in the earlier commit.

Merge remote-tracking branch 'origin/feature/8031-refactor-10-rbb-hook' into feature/8031-refactor-10-rbb-hook

Conflicts:
	config/chroot_local-hooks/10-tbb

In conflict resolution, also update to TBB 4.0 checksums and url in
tbb-dist-url.txt and tbb-sha256sums.txt.

We also instruct the RM to check the url with https for some added
authentication.

This reverts commit 7b866f52.

With the upgrade to stable TBB 4.0, all desired locales are available
again.

Conflicts:
	wiki/src/doc/anonymous_internet/i2p.mdwn

We shouldn't let the user believe that they can "configure" Firefox to be the
Tor Browser.