Handle large files in SPARQLgraph import tab

[cuddihyge]

• generic large file streaming in SPARQLgraph
• add place to drop zip files with manifest

When a file is drag-and-dropped to SPARQLgraph for uploading, it reads the whole thing into memory instead of streaming it.
This precludes large imports.
Also precludes using dropping zip files with manifests (which are usually big).

see uploadtab.js function onDropData() which is bound to the dropZones.

It seems like we ought to be able to use FormData something like stackoverflow example to stream a multipart file.