New File Uploader: file upload registration in tusd

Summary

After changing the protobuf (caosdb-proto#24)

• Implement receiving extended FileUploadRequests (+ test)
• Implement registration of file upload in tusd (+ test)
• Implement giving out upload URL for tus clients (+ test)
• Handle unreachable tusd (+ test)
• Add settings in server.conf for tusd (url pattern, proxy, port, ...)
• Update docs?