E-mails in the domain blocklist are disallowed on the admin UI, public
subscription forms, API, and in the bulk importer.
- Add blocklist setting that takes a list of multi-line domains on the
Settings -> Privacy UI.
- Refactor e-mail validation in subimporter to add blocklist checking
centrally.
- Add Cypress testr testing domain blocklist behaviour on admin
and non-admin views.
Closes#336.
- Refactor subimporter New*() funcs to take opt structs.
- Refactor and simplify Vue code.
- Remove redundant i18n entries and use existing ones.
- Remove redundant subimporter constants and use existing ones.
- Consider 'overwrite' option for subscription status as well.
- Write Cypress integration tests for the new feature.
Sending th optional flag as `trunue` in the POST /api/subscrirs
body will skip sending opt-iconfirmation e-mails to subscribers
and mark list subscriptions in the request a`confirmed`.
According to [RFC6532](https://tools.ietf.org/html/rfc6532) unicode characters are supported in email address but the in-built custom regex was only validating ASCII characters.
