When an IMAP client appends a message to a mailbox, it can specify
which flags it wants the appended message to have. We need to handle
these in a proton-specific way; not-seen messages need to be imported
with the Unread bool set to true, and flagged messages need to
additionally be imported with the Starred label.
* 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
