Upload Directly to S3

Currently, you can download from S3 by asking FC for a direct S3 download link. Provide a similar mechanism for the upload -- ie send a request for upload, send filename, file size and get an S3 location path back from from FileCloud. Client then uploads to S3 out of bounds, and at the end sends another REST request to FC to say "I'm done" with the upload.

This gets around the problem of upload scalability for FileCloud, as the all the uploading work is handled by S3. I know you can put multiple FC application servers behind a load balancer, but the direct approach will be much more performant.

This would obviously only work with S3 and not normal file system. I think this may be a relatively easy feature to implement.