Build cities list from OSM instead of Geonames #979

Fixes #979 isses with geonames timing out for large countries.
Now using a overpass API query against current OSM data, this also means
we're no longer using a dodgy bounding box to find cities, but actually
only getting cities within a country boundary.
Update i18n to include new timeout string #979
Merge pull request #985 from rjmackay/use-overpass-for-cities-979

Use overpass for cities list