exclude hidden instances from user.instances

I would have prefered to make this optional but as instances
is a property that would be complicated
hide events from hidden instances in profile page

but only if the instance is not explicitly selected.
This is consitent with how `hidden` works everywhere else.
unfinished: block notifications from hidden instances
Merge pull request #630 from xi/feature-625-hidden-infos-in-event-stream

hidden infos in event stream