Allow for the notifier to provide a 'details_filter'

When a notifier is being used for retry atoms and for
task atoms it is useful to allow a filter callback to
be provided that will skip notification depending on
whether the details matches or not (so that task or
retry notifications can proceed).

Part of fix for bug 1395966

Change-Id: If03005c253c3f540d2c33faf7a7474a5fde9dcdd
Merge "Allow for the notifier to provide a 'details_filter'"