Support grouping by different properties by label

[bechbd]

Is your feature request related to a problem? Please describe.
The current group by feature only allows you to specify a single property to group all vertices by. As a user I would like to be able to specify different properties by label to group by.

i.e. For airports I want to group by region, for country I want to group by continent.

Describe the solution you'd like
I'd like some sort of JSON type structure that would let me define something like:

{
  "airport": {"groupby": "region"},
  "country": {"groupby": "continent"}
}