It would be nice to be able to export an entire dataset and download it in one click.

We can have a button [Download zip] on the dataset view page (http://acousticbrainz.org/datasets/9cbd396f-eac7-451e-b20c-60d5ce89967e)
This button can be visible to all users, not just the owner of the dataset.

This should create a zip archive of all items in the dataset, with folders for each class and files in each folder, mbid.json

This operation may take too long for a large dataset. We need to decide if we only limit it to smaller datasets (a few thousand items?), or if we build the zip in a background process and then notify the user.