Better UI for browsing and downloading large number of files

[MLopez-Ibanez]

The current UI for browsing large number of files is not ideal and that's why users prefer to upload .zip files. However, .zip files make impossible to selectively preview and download files. A better UI would show the tree structure AND preview/download selections of files. Similar to: https://elsevier.digitalcommonsdata.com/datasets/btchxktzyw/6

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