Electricitymap-contrib: Wind stream lines density unbalanced with map scale (minor improvement)

[nvbargen]

On the wind potential map, the scaling of the wind stream line density is not balanced with the overall map scale: When taking a global view, hardly any stream lines are visible, and even big cyclone system hardly show up, whereas on a detailed scale (e.g. North Sea), even low-speed wind fields have a stream line density and length that visually would be more appropriate for a hurricane. The speed of the animation at large scale is also impressively fast (I don't get sea sick :-)).
This could probably be fine-tuned by reducing the scale sensitivity of the wind stream density (and stream line velocity).

[alixunderplatz]

@corradio @ovbm No similar issues for this stream-line related, visual topic were opened since then.
Do you want this to be fixed or leave it as it is?

[corradio]

Let's keep the issue opened for now as indeed it could be nice to have this fixed