Differentiate rendering for amenity=parking

[gormo-osm]

There could be a different symbol for amenity=parking with specific tags, e.g. hgv=designated, to differentiate parking for HGV and other motor vehicles.

Possible test case area: http://www.openstreetmap.org/#map=18/50.93985/9.54331

[kocio-pl]

1. Do we really want to have it here?
2. Any proposition how should they look like?

[pnorman]

This is a more general case of #81, and I'm 👎 on it

[kocio-pl]

Looks like too vague to make it workable. Might be reopen if something more specific would appear.