download csv files directly from datasets?

[JamesOwers]

We could implement a download_csv method in downloaders to handle direct downloading of csvs if they are avail. This is very specific to PPDD though...unless we have other datasets with csvs as opposed to midi I wouldn't bother with this.

[apmcleod]

We have empty versions of these, which we try to download first. It requires the csv to be in exactly the correct format for us (or for the loader to convert into our format on the fly). I'd probably leave it for now, and allow people to implement that for an non-MIDI format (which they'd then have to convert within the download_csv function).