Docs: convert to ISO 8601

A first attempt.
Docs: remove cold start references

And other improvements.
Fix tutorial suite syntax

Was missing `graph=`.
tutorial doc: update `rose date` offset syntax
Tutorial docs: fix duration syntax
Fix example suite syntax spacing
Tutorial doc: ISO 8601 clock-triggered syntax
Doc: update for cylc 6

Fix directory path for `work/`.
Remove unnecessary comments.
Merge pull request #1374 from matthewrmshin/doc-iso8601

 Docs: convert to ISO 8601
rose bush jobs: fix status for retried jobs

A failed job to be retried should be marked failed.
Merge pull request #1378 from matthewrmshin/fix-rose-bush-jobs-retry

rose bush jobs: fix status for retried jobs
rose.config_tree: improve pep8 and pylint scores
rose.config_tree: store file lists

If a relative path can be found in 2 or more locations in the linearised
inheritance, it will store the configuration locations in a new list.
Use rose.config_tree to load metadata

Part 1.
rose.macros.trigger: use rose.config_tree

to load metadata.