Use records and tuples for property storage

[maetl]

Although the TC39 record and tuple proposal is still at the early stages, there is a Babel implementation and seems like this would be good to explore as a long-term strategy for embedding properties on nodes and edges and implementing schema and data management features.

Even if this turns out to be unworkable, it will be useful to have established some guidance and clear thinking around this, particularly around the use of immutability and value equality.