[7117] Implement explicit recipe discovery abilities.

* Implement SPELL_EFFECT_CREATE_ITEM_2 (157). This alos let work many item creating spells.
* Add `skill_discovery_template`.`reqClass` for allow clas specific racipes storing in table.
* Make primary key for `skill_discovery_template` pair (spellId,reqSpell) that allow have duplicate recipes for different reqSpells.
* Implement SPELL_EFFECT_SCRIPT (77) cases for explicit recipe discovery spells with learn spell selected by `skill_discovery_template` data.
Note: as expected explicit recipe discovery abilities always return some spell while exist any not learned yet for player class.

src/game/Spell.cpp

@@ -3078,7 +3078,7 @@ void Spell::SendLogExecute()
                         data << uint8(0);
                     break;
                 case SPELL_EFFECT_CREATE_ITEM:
-                case SPELL_EFFECT_157:
+                case SPELL_EFFECT_CREATE_ITEM_2:
                     data << uint32(m_spellInfo->EffectItemType[0]);
                     break;
                 case SPELL_EFFECT_SUMMON: