Use SATOSHI rather than Amount construction

Summary:
The Amount constructor has the notion of satoshi built in. If we want higher precision amount in the future, we need to make that assumption in the code explicit.

As a first step Amount(1) is now SATOSHI and Amount(-1) is now -SATOSHI

Depends on D1704

Test Plan:

make check

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1705