Pushapkscript

Fixes
* `certificate_alias` is now added to the schema

Added
* New task parameter `certificate_alias`: defines the specific certificate alias that should be used to verify the APK to upload

Added
* New option `require_track`: forces any tasks matcheing the config to have the track defined in `require_track`

* Support mozapkpublisher 2.0+

Changed
* Bumps version to `1.0.0` since `pushapkscript` is used in production

Added
* New options:
* `digest_algorithm`: expected digest algorithm of signed app. Verified before app deployed to Google Play
* `update_google_play_strings`: true if strings should be updated in Google Play for this app
* `skip_checks_fennec`: passed to `mozapkpublisher`
* `skip_check_ordered_version_codes`: passed to `mozapkpublisher`
* `skip_check_multiple_locales`: passed to `mozapkpublisher`
* `skip_check_same_locales`: passed to `mozapkpublisher`
* `skip_check_package_names`: passed to `mozapkpublisher`
* `has_nightly_track`: fails build if an APK is attempted to be pushed to `nightly` without having a `nightly track

Changed
* In config, `google_play_accounts` is now called `products`