move interpolaton computation into indexing step

move interpolaton computation into indexing step

The interpolaton computation needs information from the osm2pgsql
slim tables which may not be available when the data is inserted.

Insertion now only adds a line with basic address information to
location_property_osmline. The line is then split during the
indexing, leading to more lines (which are complete in that case)
being inserted.

Fixes #598.