Core/GameObjects: Implemented gameobject_addon table, you can now set invisibility for gameobjects for quests

(cherry picked from commit 9d59d038f8b09ed036448e755cb0b102396a4ca1)

Conflicts:
	sql/updates/world/2015_04_05_07_world.sql
	src/server/game/Globals/ObjectMgr.cpp
	src/server/game/Globals/ObjectMgr.h

Core/GameObjects: fixed typo and logic (0 is a valid invisibility type)

(cherry picked from commit 23e8a3ce2928458649d94408d5deffb67339b1d6)

sql/updates/world/2015_05_19_00_world_2015_04_05_07.sql

@@ -0,0 +1,7 @@
+DROP TABLE IF EXISTS `gameobject_addon`;
+CREATE TABLE `gameobject_addon` (
+  `guid` bigint(20) unsigned NOT NULL DEFAULT '0',
+  `invisibilityType` tinyint(3) unsigned NOT NULL DEFAULT '0',
+  `invisibilityValue` int(10) unsigned NOT NULL DEFAULT '0',
+  PRIMARY KEY (`guid`)
+) ENGINE=MyISAM DEFAULT CHARSET=utf8;