Improve map

[damianooldoni]

This PR:

• Improves tile backgrounds as described by @biekemaex in https://github.com/inbo/craywatch/issues/210#issuecomment-2167882756
• Use color palette as described by @biekemaex in https://github.com/inbo/craywatch/issues/210#issuecomment-2167882756. Notice I increased the saturation of the circles otherwise the colors on the map were not always similar to the real colors in the legend.
• Reads locations following the specs as described by @fjasteen in https://github.com/inbo/craywatch/issues/210#issuecomment-2167768035
• Add absence layer called "Null waarnemingen". At the moment I use the same circles as presences. I will visualize them as markers (see #271) in a separate PR later