Separate adding and spending coins for a given transaction.

Summary:
In addition, stop enforcing transaction ordering for RollforwardBlock by adding coin and spending them in two passes.

Depends on D1478

Test Plan:

make check

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1479