Started implementing history graph (for the time being only for
temperature values)
Merge branch 'master' of https://github.com/bassages/WeatherStation.git

Conflicts:
	src/nl/wiegman/weatherstation/MainActivity.java
	src/nl/wiegman/weatherstation/fragment/SensorHistoryFragment.java
	src/nl/wiegman/weatherstation/history/SensorHistoryItem.java
	src/nl/wiegman/weatherstation/history/SensorValueHistoryDatabase.java
	src/nl/wiegman/weatherstation/history/TemperatureHistory.java