AddressBookCheckoutComponent is functional and tested

I guess I'm on the fence here. I know that javascript will make for a better user experience, on the other hand I know that more javascript means more to maintain, and somewhat means lock-in to a certain way of doing things. Will this make theming/templating more difficult?

Lets leave it in, as I don't think these issues will ever arise unless we let them.

I think if we have behat tests running with and without JS, that might help put my mind at ease. I'm guessing javascript only tests won't really help here.