Website updates

[ninadicara]

Changes:

• Updated to Python 3.9
• Removed content folder and moved hazard labels to labels.md - closes #132
• Updated to Sphinx Design from Sphinx Panels which allows alt text - closes #14
• Fixed all contributors types and added all outstanding contributors - closes #197
• Moved some of the content around to streamline the home page
• Updated the labels page to use Sphinx Design syntax and bootstrap layouts.
• Tidied up general out of date stuff and links.
• Made a new issue label for new hazard suggestions and linked to this list from labels page to direct people to leave ideas there.

In general, closes #191 - or at least happy with this as a version to work from to then add or address the other outstanding parts!