Core/Scripts/DB: remove hardcoded text from 'npc_disciple_of_naralex'

- moved 2 #define text lines to enum, already in npc_text
- new gossip_menu_option for NPC 3678 Disciple of Naralex
- using `ADD_GOSSIP_ITEM_DB` instead of `ADD_GOSSIP_ITEM`

Tested on both alliance and horde characters, works just like before.

sql/updates/world/2016_01_31_15_world.sql

@@ -0,0 +1,4 @@
+-- new gossip_menu for NPC 3678 Disciple of Naralex:
+DELETE FROM `gossip_menu_option` WHERE `menu_id`= 201 AND `OptionBroadcastTextID`= 2662;
+INSERT INTO `gossip_menu_option` (`menu_id`,`id`,`option_icon`,`option_text`,`OptionBroadcastTextID`,`option_id`,`npc_option_npcflag`,`action_menu_id`,`action_poi_id`,`box_coded`,`box_money`,`box_text`,`BoxBroadcastTextID`) VALUES
+(201, 0, 0, 'Let the event begin!', 2662, 1, 1, 0, 0, 0, 0, '', 0);