[Experience] Add exp mod to npc types to let a server op change the exp modifier (#1252)

* Add exp mod to npc types to let a server op change the exp modifier a npc gives (useful for custom content)

* Updated version.h

utils/sql/db_update_manifest.txt

@@ -413,6 +413,7 @@
 9157|2020_09_02_pet_taunting.sql|SHOW COLUMNS from `character_pet_info` LIKE 'taunting'|empty|
 9158|2020_12_09_underworld.sql|SHOW COLUMNS from `zone` LIKE 'underworld_teleport_index'|empty|
 9159|2020_12_22_expedition_system.sql|SELECT * FROM db_version WHERE version >= 9159|empty|
+9160|2021_02_14_npc_exp_mod.sql|SHOW COLUMNS from `npc_types` LIKE 'exp_mod'|empty|
 
 # Upgrade conditions:
 # 	This won't be needed after this system is implemented, but it is used database that are not

utils/sql/git/required/2021_02_14_npc_exp_mod.sql

@@ -0,0 +1 @@
+ALTER TABLE `npc_types` ADD COLUMN `exp_mod` INT NOT NULL DEFAULT '100' AFTER `always_aggro`;