Delete unnecessary sql code
Fix system dependancy bug
Refactor engine.go
Update manipulation with 'AddItem' method

Add 'AddItem' method to inventory obj. Also each of 'AddItem' method do 'SetOwner' method now.
Add 'PickUpItem' method to player. Also add user inventory and saving to db
Update item.go: add db_id to the ItemKind struct. Also add some getters and NewItem func
Restores the user equipment when entering the game. Refactor
Disabling the output of the game when client receive badId