Support imposm styles?

[hholzgra]

So far only styles that used the general osm2pgsql data schema were considered for installation, but with increasing disc capacities styles that need their own database import instead of the shared one are becoming more interesting for inclusion.

The WayMarkedTrails overlays did already sort of set a precedence here, and with the osm2pqsql "flex" backend becoming more popular the days of "everything from the same general table layout" are probably counted anyway.

So styles that use imposm instead of osm2pgsql to import OSM data should also be re-considered, e.g.:

• https://github.com/lyrk/lyrk-mapstyle
• https://github.com/tilery/pianoforte