Add a setting in the CP to define default shipping method

[nikolenko-dmitriy]

What are you trying to do?
I have 2 shipping methods on the website:

• Delivery which costs some money. In our case, we have actually 2 separate methods Delivery-Package which is free when the order total value is more than 50 Euro and Delivery-Transport which is free when the order total value is more than 300 Euro. But on the frontend only one of these methods is available, it's controlled by Weight option for the product.
• Pickup which is always free

I have to make Delivery method to be default if no shipping method is set, or the previously-selected method is not available.
But since Craft Commerce 2.0.0 the first cheapest available shipping method will be selected. And this is the problem for orders with Order Total Value is less then it's required to make Delivery method to be free, because Pickup is the cheapest method in this case.

What's your proposed solution?
I suggest either to do not select any shipping method automatically before the user makes it for himself or to create a checkmark in the Control Panel to define the default method that will be selected in such cases.

Or even better to make some kind of ordering for shipping methods using drag-and-drop functionality.
So, the shipping method that is available and has the highest position in this ordering will be selected as the default.
This would be very helpful for our case when we had to create 2 separate shipping methods for the Delivery.