Make UserModel extendable

[nilsenpaul]

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I would like to be able to extend the UserModel, in such a way that I could, for instance, let the last_login column be of type DateTime. The only thing is, that the plugin's commands use a fixed reference to yii2mod\user\models\UserModel.

If the plugin itself would have a way of configuring the model to use, then all commands would use that model. Is this something that you would be willing to pull into the code?