[bug 875313] add dennis and polib to vendor-local

This adds dennis which is a utility for linting .po files. It requires
polib.
[bug 875313] Add polint management command

This adds a polint management command which uses dennis in the django
project environment to lint .po files.
[bug 875313] Add compile-linted-mo.sh script

This uses polint to selectively compile .po files to .mo files iff
they don't have egregious errors.
[bug 875313] Use compile-linted-mo.sh in update script

This changes the update_locales part of the update script which we
use for deployments to use compile-linted-mo.sh instead of compile-mo.sh.

This will cause the deploy logs to contain a list of the files that
were compiled and the ones that are BUSTED. For now, we'll have to check
that for .po files that have errors that need to be fixed.
Adjust test_polint to be less stdout-spammy
Fix sampledata generation to use bulk_create

This makes generating large sample sets much faster.
Update dennis to 0.3.4

0.3.4 includes a fix to the linter which results in fewer false positives
when linting strings.
Add blurb about translated strings errors
[bug 898417] Add fields to Response

* adds product, channel, version and translated_description to the
  Response model
* backfills the existing data with inferred values for these fields
* updates indexing logic to use product field rather than inferring
  the value from the platform field; ditto for version
Add FirefoxOS to sampledata generator
Update admin re: recent model changes
Add second data migration to fix responses

The 0008 data migration takes a long time to run. It missed a bunch
of responses which I think were created after the sql query was
run, so the ids weren't included in the batch.

We could fix the 0008 data migration, go back and run it again, but
it's way easier to just write a new data migration to patch the
situation.
Update py-bcrypt version

This has no effect in production since we use Persona for
authentication.

However, it does affect our test system since py-bcrypt (which is
referenced in the funfactory compiled.txt file) is pegged at 0.2 and
that's not available on pypi anymore.

So updating it to fix our test system.
[bug 895675] Add django-rest-framework
[bug 895675] Implement feedback posting api
[bug 895675] Measure throttle failures

If someone bumps into a throttle failure (i.e. they were throttled), then
we want to incr statsd so we can measure how often it happens and thus
become illuminated to problems.
[bug 895675] Make trailing slash optional