This is the beginning of a library to enable simple graph visualizations in python.

2013.02.10 
It does none of the visualizing, but provides basic Graph, Vertex and Edge
classes to allow a user to represent graphs.

2013.02.25 
Finished hacking out a prototype visualization using vtk, and have included
a proof-of-concept in the __main__ test of ContributionList. There's a lot 
of redundancy and inelegance. Three priorities: add functionality to the 
visualization (mouse navigation, interactive labels); enact a better
separation of functionality between the classes; document everything.

2013.03.01
Documented everything.
Combined redundant graph classes into a single class.
removed graph internals from ContributionList.
TODO: add functionality to the visualization

2013.03.02
Added autocoloring of nodes by type--each type is randomly assigned a color;
colors are distributed evenly through the colorspace based on the total number 
of types.
Experimented with different GraphLayoutStrategies. I've been thinking about 
turning the Graph class into a subclass of vtk.MutableDirectedGraph so it's easier
to set properties without modifying the class.

2013.03.03
Added an interactor style that makes sense to me. By default, the arrow keys 
perform translation. When holding CTRL, they rotate the camera. When holding 
SHIFT, the up and down arrows zoom in and out. Right now all of the step sizes 
are hard-coded--I need to figure out a way to autoscale them based on the size
of the graph.