merge "119.iso8601 cycling" to master, for cylc-6

:guitar: for those about to rock ... :bomb: :boom:  **cylc-6**

addresses #119 
 
(there are still some details to attend to before hitting the *merge* button ... but let the review begin)
That was just to indicate, if we ever need yet another task state (god forbid!) that's a usable terminal colour control code that is not currently used (I guess it came from the former runahead task state).