Refactor internal query graph representation

[tokebe]

Previously, API response records were refactored to streamline related code interactions and to simplify testing.

It appears that our internal representation of the query graph could use a similar treatment. Currently, the query graph (as supplied by the query) is validated and transformed into first qNodes and qEdges, and then qXEdges (query execution edges) are created as a "wrapper" of sorts around qEdges. Given the actual lifetime of a qEdge and limited use outside of being part of a qXEdge, I think it makes sense to roll the two into simply just a qEdge.

Merging qEdge and qXEdge would simplify the structure and interface. Beyond this, however, refactoring the class along the lines of Record in order to allow freezing/unfreezing of an instance, where both the frozen and unfrozen data (and therefor class constructor) have the same structure and property names, would also dramatically simplify both testing and further development.

[rjawesome]

I could work on this. Some work started on combine-qedge branch (mega_query_edge.js is combined qedge/qxedge, is being used in query_graph.js).

[tokebe]

Deployed to Prod.