Enable download of datapackage as zip

[Bachibouzouk]

This enable the download of a datapackage of a scenario.

One can use the URL:
http://127.0.0.1:8000/en/scenario/export/datapackage/

Or click on "Export as datapackage" on the progession ribbon (this is just for convenience, we should have this button somewhere else)

TODO:

• Generate the datapackage.json automatically as well
• Get the foreign keys of datapackage.json correctly
• Figure out a parameter matching between open_plan parameters and the placades parameters --> this is done in Add components from openPlan tool placades#5

[Bachibouzouk]

The idea is to enable download of datapackage and then iterate to make changes to the to_datapackage method