weather: forecast up to 10 days

This service needs api key. For now I put it straightly into the url
It will need to be replaced, like in perl with {{ENV_APIKEY}} , but not sure if python supports this. Gonna look at it deeply.

Signed-off-by: Adrian Matejov <a.matejov@centrum.sk>
I didn't mean it like this, I meant it, that you would give `u'{0} -> Day: {1}\u2103 , Night: {2}\u2103 , Wind: {3} km/h ({4})'` as an argument to the method, so you would have...

    def output(self, r, diff, format_str):
        ...
        return format_str.format({'city': city, 'daytemp': daytemp, 'nighttemp': nighttemp, 'avewind': avewind, 'data': txt })

and you would call it like: `self._provider.output(r, diff, u'{city} -> Day: {daytemp}\u2103 , Night: {nighttemp}\u2103 , Wind: {avewind} km/h ({data})')`