[plugins] Change weather API to OpenWeatherMap

[obviyus]

Fixes #191.

• Now uses the OpenWeatherMap API (docs) for weather data
• By default, the API endpoint requires different parameters depending on whether the location is a city name, city id, geographical coordinates or a zip code. It might make sense to use something like geopy to get a standard lat/lon format for all locations.

[lailoken503]

Made a backup of the original plugin, and copied the update into a new plugin.py, looks like it works great, bonus that the .setw didn't need to be used again. Thanks!

[johnmaguire]

Thanks for this! There was a hiccup in that OpenWeatherMap doesn't seem to return the same location for many old queries - especially around zip codes.

I ended up implementing WeatherAPI.com as well. There's a toggle now, so either provider can be selected via configuration.