Since there are many weather services that provide an API
for fetching weather, and some don't work in other countries,
this patch adds a new service abstraction for weather.
the user configures which weather service they want to use in the config
file, then that service is loaded at start time, and the weather plugin
uses the WeatherService object to fetch the weather for a lat,lon combo.
The WeatherService itself calls the configured service object that
fetches and returns the weather. There is only 1 weather service
in this patch, which is the same as it used to be. calling
forecast.weather.gov, which is a US government API.
