initial caching thorough datastore

Description

App will show mails from cache initially until latest mails are fetched. This will give better UX when there are lots of mails are available to be fetched.

Screenshots

Technical details

Tests

Issues

backlog/-/issues/938

10 commandments of code reviews

👪 ❤ https://gitlab.e.foundation/internal/wiki/-/wikis/development/code-review