Initial hack at enabling future triggers.

Addresses #487; example in examples/future-trigger runs.
Removed misleading test suite title.
Tidied one code snippet.
Tidied another code snippet.
Merge branch 'master' into 487.future-task-triggers
Merge branch 'BugFix.HoursOfTheDay-cycling' into 487.future-task-triggers

Conflicts:
	lib/cylc/cycling/HoursOfTheDay.py
A better future trigger example suite.
Tidied offset code snippets further.
Handle future triggers in conditional expressions.
Allow shutdown with future-triggered tasks held before stop time.
Merge branch 'master' into 487.future-task-triggers
Merge branch 'master' into 487.future-task-triggers
Made polling configurable by task, with interval lists.
Completed documentation of polling.
Reordered some runtime items in the suite def reference.
Fixed new polling interval selection.

Closes #494.
Change polling interval config to minutes, and ...

...start the poll timer anew, with the second interval,
when the task enters the running state; and first interval
of 0 turns off submission polling.
Merge branch 'master' into 494-more-polling

Conflicts:
	lib/cylc/task_types/task.py
Document that delay between batches is now zero.
Separated submission and execution poll config ...

and abstracted out poll timing.