Core/Spells: Implement spell queue

Port From (https://github.com/TrinityCore/TrinityCore/commit/27019a62a4294f8dd48d975f85b1907c5adee0e3)

Source/Game/Spells/Spell.cs

@@ -8121,6 +8121,8 @@ namespace Game.Spells
             return m_casttime;
         }
 
+        public int GetRemainingCastTime() { return m_timer; }
+
         bool IsAutoRepeat()
         {
             return m_autoRepeat;