Sketch load duration plot

[jnnr]

This PR adds a load duration plot for timeseries. Timeseries for energy providing technologies can be sorted and plotted on top of each other. This should provide a quick overview of the different operation, like peak load, baseload.

TODO:

• Integrate into the snakemake workflow
• Find a more elegant solution to create a plot for all timeseries in a directory which can be adopted in plot_dispatch.py as well.
• Polish labels, colors, axes.