Add xx locale for testing

This adds:

1. xx locale which is Pirate
2. scripts/poxx.py which translates a .po file into Pirate
3. scripts/test_locale.sh which extracts strings and runs poxx.py

The xx locale is set up so that it doesn't show up in the language
chooser lists, but you can explicitly specify it in the url:

    http://localhost:8000/xx/home

The locale is only available translated locally--it will show up
as English on -dev, -stage, and -prod. It'll show up as English
if you don't run scripts/test_locale.sh.
[Bug 813472] Use addon for about:support data.

About:support data is historically rarely actually submitted, which
makes things hard. This change prompts the user to install an addon
which will automatically fill out this important field for the user.

After the addon is installed, it triggers an event, and the page fills
in the appropriate data. If the addon is already installed at page load,
it will load the data immediately.

The addon only provides this data to https://support.mozilla.org/ (NB:
SSL). To manually test this, you can launch Firefox with an environment
variable set to "bless" other urls. For example

    TROUBLESHOOTER_ORIGIN="*" firefox

Will cause all pages to have access to the troubleshooting information.
You can also give a space seperated list of urls, such as
"http://localhost:8080 http://support-dev.allizom.org".
Add extra_body_attrs handling to mobile base.html
[bug 826804] Track showfor usage in Google Analytics.
Remove old comment.

(trying to bust the CDN cache)
Update db strings.
[bug 819167] Remove email updates and rss links from question page.

Removed all the form and view code that goes along with it.
[bug 819167] More removal missing in last commit.
Cosmetic: Fix order of imports
Update tower to master tip

The version we had dated back to 2011 and didn't have fixes we made
to tower to better support Django 1.4. This updates it to include
those.
[bug #809449] Fix index name used in tests

This actually does a bunch of things.

1. Fixes the two lines that were hardcoding the index name used to
   "sumo-test" to use the ES_INDEX_PREFIX as well. This allows us
   to put the build number in the ES_INDEX_PREFIX and thus jenkins
   won't use the same index for multiple tests running at the same
   time.

2. Changes a bunch of the test infrastructure to use override_settings
   rather than settings_test.py and mocks.

3. Fixes some users app tests that were interesting.
Cosmetic: Fix pep-8 issues

We import user into the namespace, but then had a bunch of variables
also named user which is bad.
PEP-8 pass on settings.py

Mostly did this to kick jenkins into redoing my tests.
i miss u
Cosmetic: PEP-8 fixes.
[bug 836288] Add on_delete=SET_NULL to last_post FKs.

Otherwise, deleting a user that happens to be the author of last
post CASCADES to deleting the thread and/or forum.