Change the world constructor to accept owner

[glihm]

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The world constructor is currently taking the class hash of the world. However, this is something that can now be get with the new syscall.

Also, the constructor uses the account sending the transaction to avoid the UDC being the creator of the world. We should change that and pass the creator address instead, which will be easier to create a world that could be managed by marionette contract or a DAO for instance.