Filter by node or edge population `type`

[mgeplf]

When getting node and edge populations, it should be able possible to filter by type (as defined in the config file); ie: get all virtual edge populations, or only in non-virtual node populations. The idea would be that this could happen across the API.

[mgeplf]

Suggested by @MWolfR; please add more if you wish.

[joni-herttuainen]

It just about dawned on me that this is already (kind of) possible with nodes:

in h5 we have the mandatory model_type field which should conform to whatever you'd put in the Circuit Config.

Using this, we can retrieve all the certain types:

circuit.nodes.get({"model_type": "virtual"})

or the inverse of that with a "very clear" and "self-explanatory" negative lookahead regex:

circuit.nodes.get({"model_type": {"$regex": "^(?!virtual).*$"}})

this only applies to nodes, though, as edges don't have model_type.