cylc guis: fix icon for unknown state.

This fixes the icon for an unknown state - e.g. for
the submitting state that was recently renamed.

This fixes GUI-backwards-compatibility.
gcylc - handle unknown task states.
Run at/background jobs in their own process group

Re-implement job kill using the same approach as job poll.
Add dedicated test battery for job kill.
Merge pull request #1 from hjoliver/cylc-guis-fix-unknown-state-dot

gcylc - handle unknown task states.
cylc dependency graph: fix handling pre-initial over-bracketing.

This fixes a bug where unnecessarily bracketed clauses cause a crash
when they contain pre-initial cycle references. This is because the
unnecessary brackets in the graph persist through to the data structure
that is fed to the cleanup algorithm. These are now removed.
cylc dependency graph: remove debug statements
cylc runtime inheritance: catch None parents
cylc runtime inheritance: add test
cylc runtime inheritance: fix test header description
Merge pull request #823 from benfitzpatrick/catch-none-inheritance

cylc runtime inheritance: catch `inherit = None`
Merge pull request #820 from benfitzpatrick/cylc-guis-fix-unknown-state-dot

cylc guis: fix icon for unknown state.
cylc restart: fail for corrupt status in state dump
cylc restart: fix state backwards-comp.
Improve suite state dump logic

State dumps tagged with UTC time at creation.
Symbolic link "state" points to latest.
Roll using a simple FIFO logic.
Dumps from before restart are left untouched.
On restart, create a special symbolic link to point to the used state dump.
Remove some unnecessary method calls.
Merge pull request #822 from benfitzpatrick/dep-syntax.fix-pre-initial-overly-bracketed

cylc dependency graph: fix handling pre-initial over-bracketing.
Merge pull request #821 from matthewrmshin/kill-job-process-group

Run at/background jobs in their own process group
Merge pull request #824 from benfitzpatrick/cylc-restart-fail-corrupt-state-dump

cylc restart: fail for corrupt status in state dump
Merge branch 'master' into improve-state-dump

Conflicts:
	bin/cylc-restart
Merge pull request #825 from matthewrmshin/improve-state-dump

Improve suite state dump logic
Updated change log for 5.4.6.