Add parents and children to omero obj

[joshmoore]

migrate changes from: ome/openmicroscopy#4777
related discussion: https://github.com/ome/design/blob/master/OME001/index.md

[will-moore]

Trying to test locally after checking out this branch (strangely, this worked fine just now when testing #199):

$ pip uninstall omero-py
$ pip install -e .
$ omero login
Traceback (most recent call last):
  File "/Users/wmoore/opt/anaconda3/envs/omeroweb/bin/omero", line 33, in <module>
    sys.exit(load_entry_point('omero-py', 'console_scripts', 'omero')())
  File "/Users/wmoore/opt/anaconda3/envs/omeroweb/bin/omero", line 25, in importlib_load_entry_point
    return next(matches).load()
  File "/Users/wmoore/opt/anaconda3/envs/omeroweb/lib/python3.9/importlib/metadata.py", line 86, in load
    module = import_module(match.group('module'))
  File "/Users/wmoore/opt/anaconda3/envs/omeroweb/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 984, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'omero.main'

[joshmoore]

Don't think that's related to this PR.

[joshmoore]

NB: see related thoughts under https://github.com/ome/design/blob/master/OME001/index.md

[will-moore]

I realise it's not related to this PR. It just means I can't test the PR.

[joshmoore]

In coming back to this to try it myself, I realized that what I might actually want (or at least sometimes) is the entire hierarchy including intermediaries. The closest solution I could find to that was using duplicate, in case anyone has suggestions.