add a <created filter in GetForecastAsTimeseriesRequest

[peterdudfield]

In order to pull forecasts before a certain time, it would be great to add a <created filter on the GetForecastAsTimeseriesRequest route. This is for the uk-national -> quartz-api.

If we didnt want to do this, we could get the last forecast before x time, and just return those results. That would be a slight change of behaviour but this could be an option

[peterdudfield]

This is done in #103