Gantt view: colour code by cycle point

[MetRonnie]

Follow-up to #1466

At present there isn't a great deal of use in the colour coding the gantt view by task name. I had a go at making it colour coded by cycle point, and added the job ID to the tooltip

Check List

• [x] I have read CONTRIBUTING.md and added my name as a Code Contributor.
• [x] Contains logically grouped changes (else tidy your branch by rebase).
• [x] Does not contain off-topic changes (use other PRs for other changes).
• [ ] Tests are included (or explain why tests are not needed).
• [x] No changelog entry needed as follow-up to unreleased enhancement
• [x] No doc PR needed

[MetRonnie]

Bump @ChrisPaulBennett

[hjoliver]

Nice.