[Bug 845599] Fixes for a small Twitter api change.

It appears that the 'to_user_id' key is not always sent with the
response from Twitter now, and we assumed it would be. This change fixes
the cron job for me.
[bug 845582] Implement ReadOnlyBackend

Instead of wiping out all AUTHENTICATION_BACKENDS which kicks up tons
of errors, this changes read_only_mode to use the brand new
ReadOnlyBackend which categorically rejects everything.
[Bug 844933] Only use well formed troubleshooting

Instead of trying to massage and carefully tip toe aroud the parsed
troubleshooting data, this puts a filter on it so only something that
has 100% of the fields that the template uses and has all the expected
types is used. When the data doesn't match these expectations, it will
appear as plain text, unformatted. This errs on the side of not being
friendly enough, but being much safer.

Hopefully.
[bug 845608] Update django-authority to latest.
[Bug 840262] Add GA events for translation of docs

* When a document is completely untranslated, fire a "Not Translated"
  Google Analytics event.
* When a document is translated but out of date, fire a "Not Updated"
  Google Analytics event. Here "out of date" means it's parent has a
  medium or major level change.

Include medium significance edits.

Fix
[Bug 617735] Fix media gallery search field for l10n.
[bug 840966] Update commonware to v0.4.2

Also added django-statsd because the graphite related middleware moved
to that lib.
[bug 840966] Add missing X-* awesome middlewares from commonware.
[bug 840966] Migrate to Django's built-in XFrame middleware and decorators
Tweak localelinter output and verification

* take into account untranslated strings
* show the strings that were compared so it's easier to see issues
  and false positives from the output

Minor problem is that since strings are unicode and consoles might
not be, it converts strings to ascii and replaces non-ascii characters
with ? which sucks for languages that aren't ascii-ish. That needs
some thought.
Yak-shaving on the localelinter

* can now lint entire directories
* only runs on .po files
* produces stats so it's easier to see problem locales
ES_LIVE_INDEXING should default to False in tests
[Bug 794236] product.title to _(product.title ...)
Remove a blank line for new jingo-minify build id.
Add email template documentation
[bug 694941] Add UI to insert images in the contributor forums.

(/forums)
[bug 836277] Activate locale when parsing.
[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.