WIP: Cleanup benchmark charts

[WIP] In first poking around the scikit-learn code, I started by running all of the benchmarks. Not all ran, and I thought the output could be cleaned up a bit. What I've done should be pretty clear from my commit messages.

To do:
* get feedback
* make sure that plots are spaced properly not to overlap
* consider not using "tight" axis boundaries on time axes because it obscures startup time
* consider changing some axis labels from stating the measure to stating the dimension; e.g. "Samples" becomes "Dataset size (samples)"
* figure out the intention for the neighbors plot; currently two sets of plots are overlaid