Install all localized Iceweasel search plugins (Closes: #8139).

That is, except a few that we explicitly filter out.
Merge branch 'bugfix/8139-install-more-loxalized-searchplugins' into experimental
Revert "Workaround build failure in lb_source, after creating the ISO." (Closes: #5307)

This reverts commit 4218f2e47bf0ecc2bccaaed2140cc97ad6fc0ff4.

This is not needed anymore given the move to the Tor SOCKS proxy.
Merge branch 'feature/8194-APT-socks' into experimental