[ecash-herald] Use monorepo deps instead of npm

Summary:
Follow model used to successfully move Cashtab away from npm dependencies and toward monorepo hosted dependencies for packages maintained by ABC

Note: CI will be updated before landing

Test Plan:
docker build -f ecash-herald.Dockerfile -t ecash-herald_local .
./contrib/teamcity/build-configurations.py ecash-herald-tests

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D16132