Changes to improve the flexibility and compatibility with PLoS guidelines

Most figure parameters now accessible via command-line arguments. Fonts are
not, but PLoS requires Arial across the board, so that's not a problem.
Speed improvements through vectorization.

I love numpy.
Add imget to PlotUtils to get an image from FlyExpress

It assumes you already have the name of the image (not the gene), which is
accessible via a file available from the BDGP.