Added javadoc for contains() in Pile
Added empty tests for getTop(), getTop(int) and contains()
Added test for getTop in PileTest
Added test for null-return from getTop in PileTest
Fixed a bug in getTop(int) in Pile where every card in the pile would be returned instead of the requested amount
Added test for getTop(int) in PileTest
Added test for contains() in PileTest
Added test for when Pile does not cotains a card in PileTest
Added test for contains() when Pile is empty