Added optional plotting configurations.

Now you can configure the result of the `plot.py` script from an
experiment's `config.yaml` file. All the following keywords are
optional:

    color: str or hex, anything `pyplot` would understand;
    linestyle: str, also passed to `pyplot.{plot, semilogy}`;
    label: str, defaults to the config key of the particular method;
    order: number, used as a sorting key to maintain a desired
        legend order across experiments.