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/Entities/Player/Player.Fields.cs

@@ -14,6 +14,7 @@ using Game.Maps;
 using Game.Misc;
 using Game.Networking.Packets;
 using Game.Spells;
+using System;
 using System.Collections;
 using System.Collections.Generic;
 
@@ -142,7 +143,7 @@ namespace Game.Entities
         uint m_deathTimer;
         long m_deathExpireTime;
         byte m_swingErrorMsg;
-        uint m_combatExitTime;
+        DateTime m_regenInterruptTimestamp;
         uint m_regenTimerCount;
         uint m_foodEmoteTimerCount;
         uint m_weaponChangeTimer;