Set properties to original values after test

testThatWBItemCostIsWithinRange can fail if executed after
testThatWBItemCostMinAndCostMaxCanBeChanged.
Convert to XCTest

* Removed the calls to NSThread to delay in between test suites.
Set cost on newItem in playAgain

setCost was being called on currentItem before it took on the
value of newItem.  During the first round of the game, this
meant that setCost was being sent to currenItem while it was nil.