(core) Default timedOut action is to carry on as normal.

Added support in testing to check traces including timed-out targets.
(core) New FixedTimeout Scheduler.
(core) Revert default timedOutAt() behaviour

It *shouldn't* defer to completedAt() execpt in the Each case.
(core) test a couple of additional Union Schedule laws
(core) First stab at a Retry Schedule
(core) Schedule another poll after timeout.

This is to allow an actor to be resumed.
(core) Simplfy ScheduleSpec by removing redundancy
(core) Delete unused code
(core) Couple of additional Schedule laws worth checking.
Merge branch 'feature-timedout-schedules'