Initial search widget

[zwelz3]

One of the primary issues in graph exploration is the initialization of the visualization. What node(s) should be rendered to provide a starting point for exploring?

This ticket scopes in a simple search widget that scans an underlying networkx graph (created from an RDF graph via rdf2nx) for nodes that match a specific search pattern. This first version should scan well understood data (like the node label, etc.) and capture the different cases in which different nodes are returned.

This should not be hooked up to a visualization. The widget should return a set/list of nodes/edges that match the search patters (and the underlying search logic).

[zwelz3]

Current example searches for node type and edge predicate. Still need a mechanism to search through data attributes and discover single nodes.