Review artifacts in deployments package

[jubeira]

There might be some relevant missing artifacts from the latest deployments.

In general, by default we create one artifact that matches the build info name. But for pool deployments, there should be at least a pool + factory artifact (optionally with rebalancer or other auxiliary contracts).

Related with #1503; this could be standarized with the deployment.

[EndymionJkb]

What we should do ultimately depends on who is using the artifact files and for what purpose. It looked like the deployment tasks always used the build-info, but the artifacts are used in unit tests (e.g., to extract abi, bytecode, etc.)

[nventuro]

The artifacts are what is published by npm: we can't publish the entire build info as that'd be too much data (and the package should be somewhat lightweight). The artifacts should contain abi + creation code.