#119: improve documentation

This tidies up some of changes in documentation for #119.

In particular, example suites and example figures have been
updated. References to the previous date-time format have
been changed.

I also snuck in a fix for "stop after clock time" while fixing a
date-time reference in the gui...

@hjoliver, if you're available, could you take a look?

Otherwise, @matthewrmshin, please review.
This was a change to fix `cylc graph`, which failed for some of the example suites.