Dynamic resistance/modifier system

[ZakShearman]

Every EnemyMobLevel should have resistances and modifiers that can be assigned to them. However, these may need to be modified on a per-troop basis.

• EnemyMobLevel has a List
• A Resistance consists of the target tower and conditions such as X level and X modifier
• A Resistance has an apply(Tower source, float damage) method to modify damage
• A Resistance has an isApplicable(Tower tower) method to check if it can be applied to damage from X tower
  
  
  
• An EnemyMob will have a List that is modifiable within the class - if a resistance is updated and the list is the original list, it will clone the list and then proceed to modify it.