oamc: Rough addr:place= tag support.
oamc: Give max priority to addr:city in address search.

We refactor the logic of searching for a city that contains a given
address by, among other things, giving the value listed in addr:city a
higher priority than is_in ("deprecated") and boundaries or nearby
place=* nodes.
oamc: Change the street splitting min distance.

Change the maximum distance within which streets are merged together
to 10km to make search more practical.

Below the v1 patch description which is now outdated because most of
the code has changed upstream.
--
For streets longer than 900m (?) the tool would split them into
neighbourhoods assuming that those were different streets with colliding
names in the same city.  They would be displayed to the user as:
* City -> Street (Neighbourhood A)
* City -> Street (Neighbourhood B)
* etc
Users have complained that this is unpractical because often streets are
much longer.  When they search for a housenumber, they usually only
know the city, the street name, and the number, but don't know the district
name because it's not part of a written address.

It was more problematic for address nodes with "addr:place" because
those places can sometimes span 20-25km, so OsmAnd would display them
as:

* Municipality -> Village (some smaller village A)
* Municipality -> Village (hamlet B, etc.)
* etc.
Now the minimum splitting distance is set to 5km (?) for streets and
60km (?) for places.
oamc: don't redownload if file exists.