Update Sphinx panels to Sphinx design

[ninadicara]

Sphinx panels (which we use to display the labels) is no longer supported and has been migrated to Sphinx Design.
Sphinx Panels requires Sphinx < 5.0 but current version is 6.0 so it is preventing us updating generally too.

A migration guide for this is available here: https://sphinx-design.readthedocs.io/en/latest/get_started.html#migrating-from-sphinx-panels

Looks like it now uses more typical bootstrap type syntax and grid.

We should probably do this because I think it will be easier to customise the CSS so that the background colours of the panels are custom, maybe also rich text (#110), and alt-text #14.

[NatalieZelenka]

Also:

• Check if the requirements file is up to date after this change.

[ninadicara]

This issue may also allow us to finally fix the alt-text on the summary page of Hazards #14

[ninadicara]

Closed by PR #201