Persist included_in_price attributes in tax_rate spec

This took me 25 minutes to figure out.
Negative tax rate amounts (i.e. refunds) now correctly return negative amounts when they are recomputed
Remove has_available_payment validation which no longer does anything
Order shipping rates by cost ascending

This fixes a problem on the frontend that I saw where they were displaying in indeterminate ordering
[frontend] Group adjustments by their labels in checkout/_summary
Unpenderize Promotion#CreateAdjustment perform + destroy