Possibility to override Models

[gogl92]

I'm currently using MongoDB in my Laravel application, to use this extension I need the possibility to override the Models being used that way I have more control and customization of the Models that interact with Stripe Connect.

Models inside the extension should be used by default but can be override by the cashierconnect.php.

[l4nos]

I've looked at your propsoed funcationality, I will need some time to test this properly, which I do not have right now. I will merge providing this passes testing. It's used on a lot of my production environments, so I do not want to risk merging without testing.