Setup frames for labels and icon view in table header

(cityLabel, iconView, hiloLabel, temperatureLabel, conditionsLabel)
Create empty classes to retrieve weather data
Implement WXCondition's public interface
Implement WXCondition's imageName method
Add the +JSONKeyPathsByPropertyKey method that the MTLJSONSerializing protocol requires

(setup "JSON to model properties" mappings)
Add Mantle transformers for date, condition and wind speed
Override +JSONKeyPathsByPropertyKey in WXDailyForecast