Splitting shipment should update order totals/payment status

[vzqzac]

Fixes #2554, detailed issue info is in there

Here's a gif with the solution in place:

I also added a small test to make sure after calling run! in Spree::FulfilmentChanger the order is properly recalculated

[jhawthorn]

Thanks. Looks good to me.

I'd rather not have the reload, but it does seem necessary.

[vzqzac]

Thanks for your response @jhawthorn, I'd also prefer not to use it but yeah, it's necessary, in case current_shipment is deleted it is frozen at the time order.updater.update is called and causes runtime errors while trying to update item adjustments in OrderUpdater model