Enable custom styling

[iamfrank]

Enables the user to set colours individually for every type of vector on map.

Possible improvements:

• Should probably be added as a separate tab
• Not all vector layer names make intuitive sense. Maybe create logical groupings that can be coloured in one go.

[Gebuz]

I've made a few updates to the CSS.

I'm not sure how switching between the styles should interact with the custom styling. Here are a few solutions I've considered:

1. Reset all the colors to the new style when switching between styles. The downside here is that any colors the user has manually set is wiped when switching. That could be solved by saving the state for each style.
2. Create a new layer and only allow the user to edit that one. The problem here is that the user can't select their starting point. Maybe this could be a good solution if it is added to it's own separate tab combined with the ability to copy all styles from any of the styles on the style selector tab.

Other things to keep in mind:

• Some features are not in all style files so they wont show on the list by default. (for instance, see "bruges ikke": https://github.com/SDFIdk/vector_tiles_frontend/blob/main/vejledning.md#vand-) Can we solve this without a hardcoded list of all features?
• Another nice feature would be to add a save button so that the user can download the style they have created as a .json

[iamfrank]

Those are relevant improvements to consider. Let's hold back this PR until they are resolved.