fix(paohvis): improved dataMerge behavior

Performed several edits that improve the correctness of the dataMerge behavior for datasets where the row node type and the col node type differ (a future MR will address cases where rows/cols have the same nodetype and the directionality of the edges). The edits focused on the data structures for reducing nodes Ids and preserving the sorting of the hyperedge data structure to properly render the row/col headers.