Add Contribution Control to Map

[ThorntonMatthewD]

Fixes #11 and touches on #10.

Summary

Whenever at least one map layer is active a new icon will appear in the top-right corner of the map. Whenever it is hovered over (or tapped on mobile) a pop-up will appear showing the following:

• Each active map layer's name
• The contribution link for each layer (if one is available - it is omitted if absent)
• Each maintainer's name, which is a clickable link if they've provided a web address to be associated with their contributions.

Screenshots & Video

(Sorry - I tried putting them side-by-side in a couple of tables, but I could embed videos in there)

Desktop

https://github.com/hackgvl/open-map-data-multi-layers-demo/assets/44626690/b4fdac3b-5abb-4799-acc6-db1e674631fa

Mobile

https://github.com/hackgvl/open-map-data-multi-layers-demo/assets/44626690/c78d693b-b331-4a78-a736-a7811a854c8d

Testing Plan

This one is a bit more open-ended.

• [ ] Ensure that whenever there are no feature sets enabled that the maintainers icon/control is not visible.
• [ ] Whenever a layer(s) is enabled, ensure it is visible. Every layer you enable should be represented in the pop-up.
• [ ] Whenever a layer is enabled, and then disabled, it should be removed from the pop-up.
• [ ] Contribution and maintainer links should all open up new tabs whenever clicked.
• [ ] I'd encourage you to try to enable a ton of layers and make sure the scrolling/overflow aspect works. It's admittedly a bit wonky since if you use the scroll wheel on your mouse leaflet kind of hijacks that for zooming the map. For now you'll need to click-and-drag the scroll bar. :disappointed:
• [ ] Please make sure that the new elements look good at a variety of screen sizes.
• [ ] Use Lighthouse, Firefox's Accessibility Inspector, and/or whatever other accessibility testing tools (if you use something else, please let me know! I'd love to hear what you use) to make sure that this functionality can be enjoyed by as many users as possible.