use imposm3

[hixi]

If validation has been made, and imposm3 is

• faster than osm2pgsql
• yields the same data inside the database (or can be made to yield the same)
• uses less space (cache and DB) then switch to imposm3

Current state of investigation: imposm3 seems more performant and uses less cache.

Update (08.07.2016):

• imposm3 doesn't create the same schema as osm2pgsql. Might not be needed, but currently we're relying on osm_nodes and osm_ways to be imported for the address interpolation, which can't be achieved as far as I investigated. There's a pending Question on the imposm3 mailing list: https://groups.google.com/forum/#!topic/imposm/KqN-6hRM6uk