simplefs: send path notifications on subscribed folders
simplefs: send path notifications on subscribed folders

Issue: KBFS-3120

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client