Change Details

`npm test`, build node in `build` and then `BUILD_DIR="${PWD}/../../build" npm run integration-tests`

`npm test` integration tests: build node in `build` dir, then, from `bitcoin-abc/modules/ecash-wallet/`, `BUILD_DIR="${PWD}/../../build" npm run integration-tests` Review API, suggest different names, shapes of objects, anything that should go in now before we start to add more features

`npm test` integration tests: build node in `build` dir, then, from `bitcoin-abc/modules/ecash-wallet/`, build node in `build` and then `BUILD_DIR="${PWD}/../../build" npm run integration-tests` Review API, suggest different names, shapes of objects, anything that should go in now before we start to add more features