Add < operator for Card by using CardComp

Previously, to compare Card, we have to create a CardComp fctor, and use
the fctor to compare two cards. With this commit, the < operator of
Card, implemented by wrapping the CardComp, is integrated. Since
CardComp's ctor depends on prime card, within one round, after some
client declared prime, the static Card::Set_prime() should be called to
update the prime cards.