Allow Cylc Review to access Cylc 8 Workflow data.

[wxtim]

These changes partially address #4113 - Depending upon discussion on that issue, this may be a complete solution.

• Fix access to task jobs list. At this stage I have an informally tested fix. I've put it up for review so that reviewers can try it.
• Allow access to cylc.flow file. Modified the list of files so that this can be a 1-stop-shop.
• Existing tests for cylc-review don't break differently to target branch. 😢
• Create a formal test that Cylc8 Workflows can be read. Manual testing only because this a complex test for legacy software.
• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Appropriate change log entry included.
• No dependency changes.

[MetRonnie]

LGTM assuming it has at least been tested manually

[wxtim]

I'm not convinced that it's going to be particularly straightforward to automate a test for this. I think to test it manually that you should:

• Run at least 1 (but not necessarily the same) suite in Cylc7 and Cylc8.
• With cylc review open and browse around.
• Confirm that links and pages work.

[wxtim]

@dpmatthews said it worked for him on a quick test.

[datamel]

I have played a cylc 8 workflow and tested cylc review both fails on master and works as expected on this branch.
Thanks for getting me up and running with this @wxtim.
I have sent you a quick pm with the extra files from the cylc-install work.

[oliver-sanders]

Code looks good, just need to test...

[oliver-sanders]

Tested, everything working as expected.