Implement client-side spell counter for NPCs, fixes #345

Also makes all the continuous-spell-related methods in ISpellCaster default methods so they don't need implementing unless actually necessary.

src/main/java/electroblob/wizardry/entity/living/EntityShadowWraith.java

@@ -61,21 +61,6 @@ public class EntityShadowWraith extends EntitySummonedCreature implements ISpell
 		return attack;
 	}
 
-	@Override
-	public SpellModifiers getModifiers(){
-		return new SpellModifiers();
-	}
-
-	@Override
-	public Spell getContinuousSpell(){
-		return Spells.none;
-	}
-
-	@Override
-	public void setContinuousSpell(Spell spell){
-		// Doesn't use continuous spells.
-	}
-
 	@Override
 	protected void applyEntityAttributes(){
 		super.applyEntityAttributes();