https://bugzilla.gnome.org/show_bug.cgi?id=769352

Attempt to download a service.json file from gnome.org. The
file will define all information needed to create a libchamplain
source. This will help us to change the tile-server without needing
to update the application.

If the call to gnome.org fails. Fallback to a default service.json.

https://bugzilla.gnome.org/show_bug.cgi?id=769352

Older libchamplain did not have introspectable enums.
Mercator is default anyway, so do not set it.

Add mapSource.js which contains functions for creating
cached Champlain MapSources using Mapbox URI.

This reverts commit 8821328b.

The title label gets ellipsised and we do not see
the title. It seems the length of the headerbar title
does not drive the width of the dialog. This work-around
sets a minimum width of 400 for the dialog.

https://bugzilla.gnome.org/show_bug.cgi?id=756511

https://bugzilla.gnome.org/show_bug.cgi?id=756557

Make sure we do not try to add a street if the geocoding
does not produce one.

https://bugzilla.gnome.org/show_bug.cgi?id=756509

Do not travel to a contacts bounding box if the
contact only has one address.

GtkDialog overrides the suggested-action style for headerbar buttons based
on the default style. So, set the default style to get the suggested-action
style on the button.

We need to return -1  in the handler to signal that default
processing should resume.

https://bugzilla.gnome.org/show_bug.cgi?id=755521