Explicitly defining toolbar items.

[ChrisPaulBennett]

Fix issue raised in #1944

Check List

• 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).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

This does the trick for the Gantt View, however, the download button for the "box & whiskers" chart in the Analysis View still has the tooltip "Menu". The "time series chart" doesn't seem to have a download button.

[ChrisPaulBennett]

Added the changes to the box plot and time series.
FYI, you need to select some variables in the time series before the download button shows up