Add "metadata checker" to flask, making sure that the version pulled down from DV is only pulled down if a local version with the same metadata does not already exist

Currently, files are downloaded from DV no matter whether the same file is already available locally. For this issue:

[ ] Add some sort of function that pulls down the metadata from DV and compares it to local (SHA sums, perhaps, but nothing computationally intensive)
[ ] If it's available locally, then use that data.
[ ] If not, download it, and save it to a "data" folder so that we can "look" for it later
[ ] Some sort of "catalogue" of downloaded files? Maybe use pkl to optimize (note: save this for later, it's not strictly necessary

dhruvv / openod