Updated Chihuahua.java

Added class inheritance to override the feed method from Dog class.
Modified GoldenRetriever.java

Added the override for play method to change play counts to 3 in order
to change size.
Modified GreatDane.java

Added overrides to the following classes to accept larger dog size
index:
-int getSize()
-String fromSizeIndex()
-void changeSize()
Cleaned up code, removed call to super class.