XCode Stotyboard - UI wired up to viewController. Sanity check.
Unit tests pass: test_GivenSUT_WhenInputIsEmptyString_ThenReturnZero and test_GivenSUT_WhenInputIsNumber_ThenReturnNumber
Unit tests pass: test_GivenSUT_WhenInputIsEmptyString_ThenReturnZero and test_GivenSUT_WhenInputIsNumber_ThenReturnNumber