World map performance improvements

[LeoHerrmann]

I have made some changes to improve the performance of the world map (#55):

• The world map is now processed asynchronously on the client.
• Plotly, sorttable and fetch-data are loaded in the background resulting in them no longer blocking the rendering of the page.
• Scripts are only loaded on pages which need them (e.g. plotly is no longer loaded on data.html).

These changes contribute to a considerable reduction of loading times on all pages as well as the lighthouse performance score of index.html finally being in the double-digits!

There have also been some small visual changes: First of all, the marker colors look a little different now because I couldn't find a simple way of implementing them the same way as they were before. Furthermore, the layout of the labels which appear when hovering over a marker has been slightly tweaked. If you want, I could try replicating the previous look again.

Before:

After:

[LeoHerrmann]

I gave myself another try to replicate the previous color scale. The result isn't perfect but it is pretty close:

What do you think?

[BrianRuizy]

Looks good! @Rahmsauce Did add those changes to this pr?

[LeoHerrmann]

Thanks! Yes, I did.