Use default_language information from OSM

[lonvia]

We currently have hard-coded default language settings per country to help guess the language of a name tag. The OSM admin data comes with a default_language tag that might be usable for the same purpose.

Two things to be aware

• The tag works a bit different than our current default language tag: a boundary always has a single tag that may be overwritten by containing boundaries. So computation of the default language has to move into the function that computes the address and where we determine in which admin boundaries an object falls. Special cases to think about: roads crossing boundaries and POIs which don't get the full address computation treatment.
• The tag is only supposed contain a single language tag. Values with semicolon or a hyphen surrounded by spaces should be removed as faulty.