Fixed onPlay() for AdventurerCard
Fixed isVulnerableToAttack()
Fixed getOpponents()

The function was including the current player, so that was fixed.
Added SpyCard
Added ThiefCard
Added new Deck and DominionPlayer constructors

The constructors take a list of cards that make up the starting decks.
This will be useful for testing cards since buying them takes time.
Ran code formatter

Several files didn't fit the code style, so they were fixed with the code
formatter.