Add all necessary files for the multi-area model

Created by: mschmidt87

This is the pull request to add all files for the multi-area network model. It includes:

• Python scripts defining the framework
• Data processing files
• Raw data files
• Testsuite
• Figure scripts for Schmidt et al. (2017)
• Images for README

It does not include:

• Figure scripts for Schuecker, Schmidt et al (2017) and Schmidt et al (2018)
• Algorithm for the stabilization method of Schuecker, Schmidt et al. (2017)

These will be added at a later point in time.

I would like to ask @AlexVanMeegen @albada and @jschuecker to review the code. In particular, please

• Review the documentation of the scripts
• Review the scripts themselves: Do you ideas how to improve the code, how to structure it more simply?
• Try to produce all figures in figures/Schmidt2017/
• Try to run run_example.py on a cluster and on your local computer

Thanks in advance.