(core) First stab at Schedules indicating they are done.

Just enough to get everything compiling and all tests passing.  The
Union Schedule still needs work to complete it and tidy it up.
(core) A simple Take Schedule implementation.

Not added to the Schedule testing generators yet, as the Union Schedule
is still broken.
(core) tidy a little
(core) WIP Take spec
(core) Don't allow non-positive timeouts
(core) test all possible combinations of Schedules
(core) tests for the Take Schedule
(core) Smart constructor for a one-off request
(core) Smarten-up layout
(core) big oops with testing trace equality
(core) Fix a broken test
(core) Remove an invalid test

This isn't a valid law
Merge branch 'bug-trace-execution'
(core) Fill in missing implementation of Union
Merge branch 'feature-terminating-schedules'

Conflicts:
	core/src/test/scala/scheduling/CommonGenerators.scala
(core) AdhocRequest definition
(core) An actor for handling one-off requests
(core) A test for the adhoc request actor
(core) WIP refactoring data capture