Automatic download of Eurostat datasets

[cueneythizli]

This PR uses the Eurostat API to automatically download datasets and save them into the policy compass backend in the correct format.

It's possible to try to download all or only selected datasets.

To download all datasets use the "python manage.py eurostat ALL" command.
Most of the eurostat datasets will be downloaded and saved. There are still a few datasets, that will cause errors because of their different formatting, but these datasets will be skipped and the script continues with the working datasets

To download one dataset, you can use the "python manage.py eurostat " command.
For example you can use "python manage.py eurostat for_remov" to download the "for_remov" dataset.

If more datasets should be downloaded, you can add more eurostat-codes to the arguments. For example "python manage.py eurostat for_remov for_basic".