* Renaming GUI, CLI, no-impact config.
* License header and documentation rebranding.
* Rename app title and vendor. Impact: manual install
* Migrating mac keychain and launch on startup.
* Fix linter and linter renaming
- [x] write tests to check that IMAP and SMTP servers are closed when there
is no internet
- [x] always create new go-smtp instance during listenAndServe(int)