Added the unique skill "Persistence"

Miranda now has the unique skill "Persistence". Holders of this skill can last effects that fade with each turn. This means that the effects of Holy Water and Torches will not decreased until the end of the map.

This skill was inspired by Miranda's personality. Since Miranda seems to hold a never-ending grudge, like a flame that will burn forever. Needless to say, this effect is powerful because it breaks one of the rules of the game.