Add UI component for uploading zip to external data

[Xarthisius]

Add new entry in Tale view > external data > (+) menu that would:

1. open a file select dialog
2. upload a selected file via POST /dataset/importBag using parentId=tale["dataDirId"]&parentType="folder"

NOTE: requires whole-tale/girder_wholetale#502 which adds new field on Tale model (dataDirId). POST /dataset/importBag requires file in the request's body and -H "Content-Type: application/zip"