Add standard basemap that is *not* dark

[JakobMiksch]

I sometimes have trouble to recognize the features in the basemap, because I find it too dark:

Is there a possibility to also add the "standard" OpenStreetMap Mapnik style map?

Like this:

[nrenner]

Yes, that would be a doable intermediate solution for #8.

Queueing it in the next milestone, got distracted from that again.

Currently spending my achavi time/energy budget on "lobbying" for changeset-map issues to be fixed to become a full successor or code replacement.

[nrenner]

I have added additional layers on the dev instance:
https://nrenner.github.io/achavi/

Example dataset (for low zoom):
http://nrenner.github.io/achavi/?url=http://norbertrenner.de/share/charging_stations.xml.gz

The "pale", "gray" and "inverted" layers are using CSS Filter Effects on the OSM standard tiles (might still do some tweaking). Not sure if there are too many options now.

Feedback welcome.