Labels can be held locally and updated in memory. This greatly improves
the responsiveness of IMAP mailbox operations as we don't need to fetch
all a user's labels to find the parent whenever a mailbox is moved.
This fixes various race conditions and leaks related to the user's sync
and API event stream. It was possible for a sync/stream to begin after a
user was already closed; this change prevents that by managing the
goroutines related to sync/stream within cancellable groups.
Add missing Close calls.
Properly handle nil channel for `user.startSync`.
This patch also updated liteapi and Gluon to latest master and dev
version respectively.
We need to unlock the user keyring anyway to unlock the address keyring,
so we should just return it instead of re-unlocking the user keyring
when sending a message.
