Build OrderSubmitted as a EventSummary

[andrzejkrzywda]

The goal is to then have consumers use this event.
Then we can get rid of Ordering::OrderLines because they are only used for the need of this event.

Also, it will help to eliminate some "processes".

[pjurewicz]

Then we can get rid of Ordering::OrderLines because they are only used for the need of this event.

It turns out that there is one invariant that takes advantage of order_lines:
raise CannotRemoveZeroQuantityItem if @basket.quantity(product_id).zero?

[andrzejkrzywda]

I don't think this is an important feature. We can move it to somewhere else (pricing?) or get rid of it.