[Bug 827651] Localize questions list.

This filters questions to only the current language for locales that
have opted-in to AAQ localization. For languages that have not opted in,
it filters by English and by the current Locale, so they don't see
questions specifically marked for other locales.

I chose this because it most closely duplicates the current behavior of
the question list for non-AAQ locales. Before AAQ localization,
questions in the question list would show only English, because that was
the only available locale. This duplicates that behavior.
Cosmetic: Remove unused imports
Add autoescape extension to Jinja config

We need this for email templates.
Add send_messages convenience function to email_utils
[bug 846386] l10n the kb email templates

* overhaul code to support setting the right locale for each user
  for each email sent
* convert kb email templates from Django to Jinja2
Add autoescape wrappers to users app email templates

The emails are text-based, so this prevents html escaping which makes
it difficult to read them.
Add autoescape wrapper to questions email templates

Emails are text-based, so it's weird to be html escaping them.
Import document_tools with context for csrf.