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.
Merge pull request #1 from hjoliver/cylc-guis-fix-unknown-state-dot

gcylc - handle unknown task states.
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.