Inconsistent names

[sorokya]

Mostly a brain dump of things I found weird

• welcome_code not welcome_reply (all other reply packets use the x_reply naming

• spell vs skill (should stick with skill I think)

• item vs buy_item sell_item drop_item etc (think we should keep it simple and just use item)

• base and secondary vs base_stats and secondary_status

• NpcType::Trainer should be SkillMaster ?

• victim vs target (victim doesn't really make sense for heal spells

• level_up should be level_up_stats in npc packets

• ChestReply server packet could use Item rather than item_id and remaining_item_amount

Will add more later probably. Ignore until I let you know it's complete :P