Add functionality to make sortable listviews

[jemayn]

We use UI Builder a lot for managing external data in the backoffice that is then shown on the website.

Our editors often has a request to sort the lists manually - we can add a sort property and have them manually fill them out with some logic to handle sort number conflicts, but it would be super nice if UI Builder has support for sorting listviews and then saving the new sort number after dragging the order around a bit.