bc2pg - record geometry type?

An empty table can be created fairly quickly with `bcdata bc2pg -e -c 1 `, but this still takes a bit of time to round-trip from WFS. For automated testing and generation of db setup scripts, a `bc2pg` option for emitting only `create table` SQL would be useful (rather than creating the empty table).

The table is defined by the catalogue api - apart from the geometry type. If we record known geometry types the request to WFS should not be required for defining the table / generating sql.