Core/Units: Power handling improvements

* Don't include creature_template power multipliers in CreateMana updatefield
* Allow NPCs to have power types other than mana
* Add missing Essence config regeneration rate
* Fixed demon hunter powers not decaying immediately after combat
* Fixed some powers decaying immediately out of combat after energizing (for example holy power)
* Replace hardcoded list of powers to set to full on levelup with a db2 flag check
* Updated Creature::GetPowerIndex for 10.1 new power types
Port From (https://github.com/TrinityCore/TrinityCore/commit/1325e0c4b279d590acbcbb05d6abdf5fdb66a882)

Source/Game/Networking/Packets/CombatPackets.cs

@@ -178,6 +178,21 @@ namespace Game.Networking.Packets
         public List<PowerUpdatePower> Powers;
     }
 
+    class InterruptPowerRegen : ServerPacket
+    {
+        public int PowerType;
+
+        public InterruptPowerRegen(PowerType powerType) : base(ServerOpcodes.InterruptPowerRegen, ConnectionType.Instance)
+        {
+            PowerType = (int)powerType;
+        }
+
+        public override void Write()
+        {
+            _worldPacket.WriteInt32(PowerType);
+        }
+    }
+    
     public class SetSheathed : ClientPacket
     {
         public SetSheathed(WorldPacket packet) : base(packet) { }