Review EOS TUS implementation and understand interplay with tusd lib interfaces

[labkode]

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[ishank011]

@butonic @labkode the way in which we were handling tus uploads was inefficient. Like you mentioned here, owncloud/ocis#997 (comment), even in the tus workflow, we were assembling all the chunks locally on the storageprovider machine and then copying the assembled file to EOS. This is also the way we handle v1 chunking which isn't ideal either.

EOS now has support for handling HTTP requests directly and the logic for combining the chunks, which I'm working on connecting now. Once we have that, we could directly forward the requests, making it a much better approach. So we could enable TUS again once that is done.