Adding support of filter function to find_nearest_city method

Add new api named find_nearest_city_full similar to find_nearest_city
and take new argumnets to take filter function from the app and the filter
function return true to continue checking for the location and
returns false to filter it out.

https://bugzilla.gnome.org/show_bug.cgi?id=726186
New api with the support of geocoding to find_nearest_city

Use geocoding to get the nearest place and using that geocode place
looks for the nearest city that lies in the same country and return
the newly created detached location using current location name and
coordinates and metar code of the nearest weather station.

https://bugzilla.gnome.org/show_bug.cgi?id=725842