New gcylc text view column layout.

And icons for task filter checkbuttons.
Restored state column.
Update documentation.
Add missing line for final cycle point.
Initialise process pool early

Move "process pool size" setting from suite to site/user.

Reduce memory footprint at point of fork to reduce memory footprint at
the start of each child process.
Merge pull request #1100 from hjoliver/gcylc.new-textview-columns

New gcylc text view column layout.
Merge pull request #1103 from matthewrmshin/init-process-pool-early

Initialise process pool early
Merge pull request #1101 from arjclark/doc.add_chaining_mention

Documentation: discuss chaining offsets in cycle point offset
Added the "definition order" sort algorithm test to the dev dir.