Added Uses arrow between UserInterface and WeatherStation.
Added test for setTemperature in the TemperatureSensor.
Added MockSensorObserver to allow me to test SensorObserver without
needing to tie the tests to one specific implementation of
SensorObserver. 

Added ability to have a single observer added or removed to
TemperatureSensor.
Implemented notifyObservers in TemperatureSensor.
Created test class for WeatherStation.
Implemented test for the observer pattern in the WeatherStation.
Created mock weather observer and am checking notification chain from
temperatureSensor -> WeatherStation -> WeatherObserver.
Added simple activity pattern.