[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/SharedDefines.h

@@ -675,7 +675,7 @@ enum SpellEffects
     SPELL_EFFECT_154                       = 154,
     SPELL_EFFECT_TITAN_GRIP                = 155,
     SPELL_EFFECT_ADD_SOCKET                = 156,
-    SPELL_EFFECT_157                       = 157,
+    SPELL_EFFECT_CREATE_ITEM_2             = 157,
     SPELL_EFFECT_MILLING                   = 158,
     SPELL_EFFECT_ALLOW_RENAME_PET          = 159,
     TOTAL_SPELL_EFFECTS                    = 160