display message on entity summary when a problem exists;
fix the activity JS so that it shares code for the panel,
and so it reads (and writes) backbone history for task navigation,
with links to that navigation from the entity summary message;
we now prefer the format `#v1/route` over `#/v1/route/` with backbone (which it seems to prefer);
and REST API includes isError and isCancelled for TaskSummary.