Shows off some of the capabilities of `PluggableRenderer`. This code provides examples of different ways to provide and change the various functions that provide property information to the renderer.

This demo creates a random mixed-mode graph with random edge weights using `TestGraph.generateMixedRandomGraph`. It then runs `VoltageRanker` on this graph, using half of the "seed" vertices from the random graph generation as voltage sources, and half of them as voltage sinks.

What the controls do:

"vertex seed coloring": if checked, the seed vertices are colored blue, and all other vertices are colored red. Otherwise, all vertices are colored a slightly transparent red (except the currently "picked" vertex, which is colored transparent purple).
"vertex selection stroke highlighting": if checked, the picked vertex and its neighbors are all drawn with heavy borders. Otherwise, all vertices are drawn with light borders.
"show vertex ranks (voltages)": if checked, each vertex is labeled with its calculated 'voltage'. Otherwise, vertices are unlabeled.
"vertex degree shapes": if checked, vertices are drawn with a polygon with number of sides proportional to its degree. Otherwise, vertices are drawn as ellipses.
"vertex voltage size": if checked, vertices are drawn with a size proportional to their voltage ranking. Otherwise, all vertices are drawn at the same size.
"vertex degree ratio stretch": if checked, vertices are drawn with an aspect ratio (height/width ratio) proportional to the ratio of their indegree to their outdegree. Otherwise, vertices are drawn with an aspect ratio of 1.
"bold text": if checked, all vertex and edge labels are drawn using a boldface font. Otherwise, a normal-weight font is used. (Has no effect if no labels are currently visible.)
"edge weight highlighting": if checked, edges with weight greater than a threshold value are drawn using thick black solid lines, and other edges are drawn using thin gray dotted lines. (This combines edge stroke and color.) Otherwise, all edges are drawn with thin black solid lines.
"show edge weights": if checked, edges are labeled with their weights. Otherwise, edges are not labeled.
"show undirected edge arrows": if checked, undirected edges are drawn with arrowheads at each end. Otherwise, no arrows are used for undirected edges.