Weather conditions - at least as far as online services are
concerned - don't usually change in a couple of minutes.
So when updating shortly after a previous update, assume
the current conditions are still valid and trigger an
update without showing a loading indication. This should
help a bit with not getting stuck permanently in loading
state when on a shitty network.
https://bugzilla.gnome.org/show_bug.cgi?id=754031
In preparation of integrating GNOME Weather, add a helper class that
retrieves weather information according to Weather's configuration
if the application is installed.
https://bugzilla.gnome.org/show_bug.cgi?id=754031
