Lazy load the cart block

I prefer the second version better with the service as that allows overridding the logic easily.
We might need a change record for that change though, other than that, perhaps I should test this manually as well, I just reviewed the code which looks ok at first glance.

Also since CartBlock::getCartViews() is unused, it can be safely removed as it is not a public method.

Automatically closed - issue fixed for 2 weeks with no activity.