weather: Rework weather management

This commit brings a few changes that I was too lazy to
split in different commits:

 * Remove a few useless arguments in the GcalWeatherService API
 * Move the weather management code from GcalWindow to GcalWeatherSettings
 * A few style changes

src/weather/gcal-weather-settings.h

@@ -0,0 +1,36 @@
+/* gcal-weather-settings.h
+ *
+ * Copyright © 2018 Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "gcal-weather-service.h"
+
+#include <gtk/gtk.h>
+
+G_BEGIN_DECLS
+
+#define GCAL_TYPE_WEATHER_SETTINGS (gcal_weather_settings_get_type())
+
+G_DECLARE_FINAL_TYPE (GcalWeatherSettings, gcal_weather_settings, GCAL, WEATHER_SETTINGS, GtkBox)
+
+GcalWeatherService*  gcal_weather_settings_get_weather_service   (GcalWeatherSettings *self);
+
+void                 gcal_weather_settings_set_weather_service   (GcalWeatherSettings *self,
+                                                                  GcalWeatherService  *service);
+
+G_END_DECLS