OSM: Honor min/max zoom level limits coming from the provider records

This patch prevents the tile fetcher from requesting tiles with a
z values that is outside the range defined in the provider record.
If the provider record does not specify these values, the default
values are used (0 and 20)

Change-Id: I5c3f7be8bbd2b2ce6c8c8d6d8d81431237e60f5b
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>