Use new /sign/file autograph endpoint (mozilla#10457)

Fixes #9308

Various cleanups along the way, this PR is porting some code over from signing-clients so that we'll be able to remove that dependency once we don't have to do the actual signing on our end anymore.

I'm also renaming crypto/packaged.py into crypto/signing.py since it feels more fitting.

* Remove utterly misplaced migration
* Rename crypto.packaged -> crypto.signing
* Port SignatureInfo over from signing-clients as we'll be able to get rid of that dependency soon
* Actually implement the new /sign/file endpoint.
* Upgrade autograph for travis to 2.7.0
* Split autograph signing endpoint usage, add migration

lowercase the locale in LANGUAGES (mozilla#10440)

Extract new versions asynchronously into git-storage.

Fixes #10408

have command to only regenerate missing theme previews (mozilla#10400)

have command to only regenerate missing theme previews (mozilla#10400)

correctly generate parent folders for preview image files (mozilla#10360

)

Fix parameters ordering when calling call_recommendation_server()

This fixes the add-on recommendation API

Pontoon: Update Russian (ru) localization of AMO

Localization authors:
- Alexander Slovesnik <unghost@mozilla-russia.org>
- Victor Bychek <a@bychek.ru>