Remove export path from menu.svg.

Fuck Inkscape.
Add OpenStreetMap Nominatim geocoder.
Remove viewbox arguments from geocoders.

This is too mysterious as the user cannot really know that the viewbox
is somehow (how?) preferred. The additional URL parameters also make
caching results within session difficult.
Always send limit=20 to Nominatim.

It's probably not much slower than limit=1, but makes our own caching
work better.
Remove nmax argument from geocoders.

It's not really significant.
Defer the Nominatim problem.