More uniform fields

[jefferis]

It would be useful to add more fields that are uniformly available across datasets. The following

• sex (obvious from the dataset, but I think better to have directly returned)
• organ (or tissue or division or some such).
  • Could be brain or VNC.
  • Should it be based on somatic origin? or synapse overlap?
  • If synapse overlap, we need to represent both: CNS?
  • how about sensory neurons: same?

[jefferis]

I think this should be soma based e.g. soma_division and there should be options for e.g. head and body to handle sensory neurons. But body strictly refers to the whole thing, so we might need to say thorax+abdomen which is a bit unwieldy.

[jefferis]

That said, for CNS datasets it would frequently be helpful to resolve connectivity into brain vs VNC. So soma_division works well for metadata, but for cf_partners() some kind of synapse_location should perhaps be returned.