Build against gweather-4.0

Will Thompson requested to merge wjt/gweather-4 into master

GWeather 4.0 removes GWeatherLocationEntry and, as a result, its dependency on any version of GTK. It also makes some breaking API changes.

Adjust to those changes, and import & adapt a copy of GWeatherLocationEntry.

Fixes #132 (closed)

Edited by Will Thompson

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