Add `data_preparation/generate_customers.py`, a script that takes the
`base_data.json` file generated by `get_base_data.py` and randomly
samples a given number of customers.
To simplify things, each customer is assigned exactly one gas and one
electricity meter and each of them is read between 1 and 10 times.
The full data including meters, meter readings and dates as well as
customers and addresses is stored in a final JSON file named
`customers.json`.
The script `get_base_data` takes the raw datafiles (such as `names.txt`)
and formats them in a common JSON file, which can be later used to
randomly generate customer and meter readings data.
Additionally, the script filters all eligible zip codes an approximate
avacon netz service area and provides some additional information for
them.
An example output file, `base_data.json` has been added to the repo in
a previous commit.
