Restructure suite run time log/job/ and work/

Directory structure now looks like:
* `log/job/CYCLE/TASK/{01,02,...,NN}/{job,job.out,job.err,job.status}`
* `work/CYCLE/TASK/`

which should make it easier to archive the log for the whole cycle or to
housekeep all the work files of a given cycle.

`log/job/CYCLE/TASK/NN` is a symbolic link that points to the job log
directory of the latest submit for `TASK.CYCLE`.
log/work restructure: fix combo log view

It was displaying only the base names of the files, which would not be
very meaningful when we have multiple submits.

Rename CYCLE_TIME to CYCLE_POINT in `cylc.cfgspec.suite`.
Log/work restructure: fix test
Script to upgrade a pre cylc-6 suite run dir.
Merge pull request #1069 from matthewrmshin/log-work-restructure

Restructure suite run time log/job/ and work/