Add superclass for WetterDaten

src/wetterstation/AktuelleBedingungenAnzeige.java

src/wetterstation/EigenschaftenSubjekt.java

src/wetterstation/SensorDaten.java

src/wetterstation/StatistikAnzeige.java

src/wetterstation/VorhersageAnzeige.java

src/wetterstation/WetterDaten.java