Mozapkpublisher

Added
* Support Google Play's new `internal` track
* Support Firefox Focus/Klar APKs. Specific tests for these APKs were added.

Changed
* `push_apk()` has its command line arguments changed.
* There is no need to precise the package name and the architecture anymore. These values are automatically extracted and checked from the passed APKs. As a consequence, APKs are now (unordered) positional arguments.
* `--track` is now required and doesn't default to `alpha` anymore.

Added
* More data is extracted from APKs and checked.
* Namely: processor architecture, Firefox version, Firefox buildId, locales, Android package name, Android API level, Android version code.
* `mozapkpublisher.apk` was split in favor of `mozapkpublisher.apk.{extractor,checker}`
* `mozapkpublisher.apk.extractor` relies on androguard to extract Android specific data
* It works with a copy of the APKs, in the (very unlikely) case the APK gets modified by the extracting function
* `mozapkpublisher.apk.checker` verifies the common values are all identical and the different ones are correctly order and none is missing.
* `Base` parser now accepts positional arguments in parameters dictionary. They must be filled as `{'*args': [positional_arg_1, positional_arg_2, positional_arg_3]}`

Removed
* Python 2 support has been droppped. Handling unicode strings in both Python 2 and 3 became too risky for the [pros Python 2 gave](https://github.com/mozilla-releng/mozapkpublisher/pull/45).

Added
* get_l10n_strings.py now exists. It fetches strings from the Google Play store for later use (by push_apk.py).

Changed
* push_apk.py
* You now need to provide where the Google Play linsting are taken from (`--update-gp-strings-from-l10n-store`, `--update-gp-strings-from-file`, or even `--no-gp-string-update`).
* Google Play strings are now verified: Data structure must comply to a given schema. Actual strings aren't checked.
* Option `--dry-run` becomes `--commit`. By default, no transaction is committed.
* Option `--do-not-contact-google-play` was added. It allows to run the script without making any call to Google.
* Non-script files are moved to `mozapkpublisher/common.`

Changed
* Dawn project
* Publish Nightly on top of Aurora
* Fetch and upload Nightly listings/recent changes
* Optimize network requests on both stores_l10n and Google Play ends
* Remove the ability to download Aurora APKs

Fixed
* get_apk.py: Fix checksum detection when file is in a subfolder

Changed
* Upgrade upstream dependencies