refactor: :recycle: Add from_id classmethod to Asset and Node classes

[joconnor-ecaa]

Description

Remove API calls from init methods in Node and Asset classes and move into from_id classmethod. Trying to make init able to construct both directly from data as well as from partial data + API call was leading to unnecessary complexity. We now leave the init class for directly instantiating via the inherited schema init and explicity call from_id or search to retrieve from the API.

Checklist

• [x] Dependencies install correctly in a clean environment and code executes;
• [x] Test coverage extended; created tests fail without the change (if possible);
• [x] All tests passing;
• [x] Commits follow a type convention (e.g. https://gist.github.com/brianclements/841ea7bffdb01346392c#type);
• [x] Extended the README, documentation and/or docstrings, if necessary;

[joconnor-ecaa]

Waiting for PR #28 to be merged to update node tests

[Lkruitwagen]

fix from_id when #28 done