Add Yahoo Weather support. Still needs to listen to the provider

I have added support for Yahoo Weather API since OpenWeatherMap have a problem in my area. The code is based on the Simple Weather watchface https://github.com/tallerthenyou/simplicity-with-day/ but I changed it to not use the Flickr API to get the location and use the Official Yahooo Placefinder API. 
There is one thing left to do and that is to hook up the settings and make it selectable, but I left that to you since you control the settings html page.