Manually create vegalite specs for all visualisations

[KleinRana]

• Number of concerts per year
• Distribution over musical genres
• The top ten creators, based on number of concerts
• The top ten performers, based on number of concerts
• Number of concerts per location
• The top ten production companies, based on number of concerts

[Veldhoen]

After looking around for a bit, I don't think vega-lite allows you to use an image as fill, like in the top x creators bubble chart

[Veldhoen]

Creating a map visualization is harder than you would think :')

I used a (somwhat) low-res Geopackage of the Dutch municipalities from here: https://data.overheid.nl/dataset/29b308ad-8e50-43ae-b5a5-4df68f109310 (CC-0 license)
I transformed it to geojson, using the appropriate projection, using ogr2ogr: ogr2ogr -f GeoJSON gemeentes_NL.json <geopackage-file> -t_srs epsg:4326
Now vegalite can be used to plot the map

Possible improvements:

• Do not load data from github raw URL but locally
• Use a nicer map (this one has municipality borders, which also have water included)
• Add all of the concert venues (rather than the top 10)
• Deal with missing locations