Add special case handling for draft messages so that if a Draft is
updated via an event it is correctly updated on the IMAP client via a
the new `imap.MessageUpdated event`.
This patch also updates Gluon to the latest version.
It's possible (but very rare, I don't think proton still allows it)
for an address to have no keys. If we try to load the address keyring
for such an address, this change logs a warning that no decryption
entities were found in the unlocked keyring.
It bumps liteapi to a version that does not return an error when no
keys could be unlocked.
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.
