Add support for more weather engines

[krnekhelesh]

As of now, stormcloud only uses yahoo engine. It would be nice if it supported other engines cloud google, accuweather, open weather app. This issue was raised in the comments in the omgubuntu post by some users. I think it is a valid concern since in some countries, yahoo weather is not that accurate.

[consindo]

Pricing is the problem. The Ubuntu Software Center doesn't monetize very well to use fancy APIs like Dark Sky or Wunderground.

I'll do some analytics in the next version, seeing how many api calls are done via Stormcloud each day and seeing how much it would cost.