Support data other than GeoFabrik (ex: no refs)

[emi420]

The bootstrap process needs to create validation tables and analyze the schema to see if there are refs or not. Also if there are tables for lines, nodes and ways or not, so it can support the processing of databases other than the one produced by importing a PBF file download from GeoFabrik.

[robsavoye]

The osm-rawdata python module has a class "MapImporter" that'll read external data sources into the Underpass schema. I used this to import Overture data, and then ran the Underpass data quality checks on it.