The sidebar had two separate watchers checking for a change in the
current user ID and focused group, each of which independently called
`loadAnnotations`. Therefore if both changed at the same time,
annotations could be loaded twice. This happens when logging out if a
private group was selected prior to doing so, since the group switches
to "Public" at the same time as the userid becomes `null`.

This commit fixes the issue by consolidating the check for a change in
group ID and a change in user ID into a single watcher. If either or
both change, `loadAnnotations` will only be called once.