Refactorize weather widget implementation

Simplify WeatherUpdateService and introduce 2 workers:
- OneTimeWeatherRequestWorker
- ForceWeatherRequestWorker

WeatherUpdateService schedules every 10 seconds a
OneTimeWeatherRequestWorker that checks if a weather request
is needed according to the period set in the widget settings.
Default period has been adjusted to 15 minutes.

The widget update button triggers a ForceWeatherRequestWorker
which forces a high accuracy location request.