Investigate small-scale widgets for initial exploration of RDF graphs

[zwelz3]

During development on #91, issues related to visualization of large RDF graphs (and networkx graphs) became apparent. Cytoscape and Datashader struggle to render extremely large graphs, which makes it difficult to interact with them (especially when load times are >30s).

It is becoming apparent that (in python+jupyerlab) we need a way to iteratively explore graphs, starting with smaller numbers of nodes, and providing intelligent ways to traverse the graph. The GraphExplorer work (#75) was a good first step.

This ticket will investigate:

• proper way to render potential paths from a source node
• potentially valuable ways to filter the initial population of nodes
• changing node/edge classes on selection (for emphasis)

Blocked by #91 (and zwelz3/widget-updates)