If the install handler goroutine is busy, the update is dropped.
This was intended to prevent two installs from happening at once.
However, it also means that updates can be dropped at startup if the
goroutine isn't spawned soon enough.
A fix is to allow all jobs through and just reject ones that are
for an old version.
Depending on the timing of bridge closure, it was possible for the
IMAP/SMTP servers to not have started serving yet. By grouping this in
a cancelable goroutine group (*xsync.Group), we mitigate this issue.
Further, depending on internet disconnection timing during user login,
it was possible for a user to be improperly logged in. This change
fixes this and adds test coverage for it.
Lastly, depending on timing, certain background tasks (updates check,
connectivity ping) could be improperly started or closed. This change
groups them in the *xsync.Group as well to be closed properly.
