fossid-webapp: Support scans with file upload

[nnobelis]

In the current implementation, we give a GIT repo URL to FossID and the instance downloads the code and scans it.

There is a second possibility in FossID API: through the api_upload_endpoint.php, it is possible to upload source artefacts and order FossID to scan them. We should implement this behaviour.

This would also allows us to create project zips with some components manually excluded (e.g. output from downloader) and scans them.