forward: make answer_count a property

https://bugzilla.gnome.org/show_bug.cgi?id=719585
Add new object GeocodeBoundingBox

Add an object representing a geographical area.

https://bugzilla.gnome.org/show_bug.cgi?id=719585
forward: add search area property

Nominatim allows searches to be limited to a viewbox. In
order to take advantage of this we need a new property.

The search area is specified as a GeocodeBoundingBox.

https://bugzilla.gnome.org/show_bug.cgi?id=719585
forward: add bounded property

The bounded boolean property decides if the search-area property
sets an hard limit or not. If false the search-area is simply the
prefered area for search. If true it restricts results to only items
within the search-area.

https://bugzilla.gnome.org/show_bug.cgi?id=719585