* now uses the same permission model as for the activity feed:
only include activities in repos, that the doer has access to.
this might be somewhat slower.
* also improves handling of user.KeepActivityPrivate (still shows
the heatmap to self & admins)
* extend tests
* adjust integration test to new behaviour
* add access to actions for admins
* extend heatmap unit tests
f6bec85296