Core/Spells: spell effect handling improvements

* Call spell effect handlers in 4 modes:
   - SPELL_EFFECT_HANDLE_LAUNCH - called when spell is launched (cast just finished)
   - SPELL_EFFECT_HANDLE_LAUNCH_TARGET - called when spell is launched for each target in spell target map
   - SPELL_EFFECT_HANDLE_HIT - called when spell hits its destination
   - SPELL_EFFECT_HANDLE_HIT_TARGET - called when spell hits it's target from spell target map
*Correctly implement SPELL_EFFECT_TRIGGER_SPELL, SPELL_EFFECT_TRIGGER_SPELL_WITH_VALUE, SPELL_EFFECT_TRIGGER_MISSILE_SPELL_WITH_VALUE, SPELL_EFFECT_TRIGGER_MISSILE_SPELL
*Remove spell system hacks which became obsolete with this commit
Core/SpellScripts:
add OnEffectLaunch, OnEffectLaunchTarget, OnEffectHit, OnEffectHitTarget hooks for new effect handle modes and remove OnEffect hook.
A generic rule of thumb how to update your scripts (will work for nearly all cases) for spell system noobs:
if your spell script used GetHitXXXX function, you need to use OnEffectHitTarget, otherwise use
OnEffectHit

src/server/scripts/Spells/spell_warlock.cpp

@@ -148,7 +148,7 @@ class spell_warl_demonic_empowerment : public SpellScriptLoader
 
             void Register()
             {
-                OnEffect += SpellEffectFn(spell_warl_demonic_empowerment_SpellScript::HandleScriptEffect, EFFECT_0, SPELL_EFFECT_SCRIPT_EFFECT);
+                OnEffectHitTarget += SpellEffectFn(spell_warl_demonic_empowerment_SpellScript::HandleScriptEffect, EFFECT_0, SPELL_EFFECT_SCRIPT_EFFECT);
             }
         };
 
@@ -204,7 +204,7 @@ class spell_warl_create_healthstone : public SpellScriptLoader
 
             void Register()
             {
-                OnEffect += SpellEffectFn(spell_warl_create_healthstone_SpellScript::HandleScriptEffect, EFFECT_0, SPELL_EFFECT_SCRIPT_EFFECT);
+                OnEffectHitTarget += SpellEffectFn(spell_warl_create_healthstone_SpellScript::HandleScriptEffect, EFFECT_0, SPELL_EFFECT_SCRIPT_EFFECT);
             }
         };
 
@@ -245,7 +245,7 @@ class spell_warl_everlasting_affliction : public SpellScriptLoader
 
             void Register()
             {
-                OnEffect += SpellEffectFn(spell_warl_everlasting_affliction_SpellScript::HandleScriptEffect, EFFECT_0, SPELL_EFFECT_SCRIPT_EFFECT);
+                OnEffectHitTarget += SpellEffectFn(spell_warl_everlasting_affliction_SpellScript::HandleScriptEffect, EFFECT_0, SPELL_EFFECT_SCRIPT_EFFECT);
             }
         };
 
@@ -267,12 +267,12 @@ public:
 
         void HandleDummy(SpellEffIndex /*effIndex*/)
         {
-            GetCaster()->CastSpell(GetHitUnit(), GetEffectValue(), true);
+            GetCaster()->CastSpell(GetCaster(), GetEffectValue(), true);
         }
 
         void Register()
         {
-            OnEffect += SpellEffectFn(spell_warl_ritual_of_doom_effect_SpellScript::HandleDummy, EFFECT_0, SPELL_EFFECT_DUMMY);
+            OnEffectHit += SpellEffectFn(spell_warl_ritual_of_doom_effect_SpellScript::HandleDummy, EFFECT_0, SPELL_EFFECT_DUMMY);
         }
     };