Added Effect skill and MaxCombatDistance tag

Added MaxCombatDistance Tag (cannot damage boss if you are further away than the specified distance). Helps protect bosses from long-range bow sniping...
Added Effect skill and "Sound" effect to go along with it, will add more effects in the future... sound effect plays a sound from the resource pack.

Usage:
  - effect TARGET EFFECT effectoptions >0 1
  
Target can be boss or player right now.
  
Sound effect has options path.to.sound:volume:pitch

Example:
  - effect boss sound mob.zombie.say:2:2 >0 1