Revise file upload logic.

[bschroeter]

Following an email from Gavin today, the file upload issue appears to be resolved. However, the API endpoint has changed as per the openapi.json for the service. The following work needs to be done to bring the client back up to spec.

• [x] The file upload is now api/upload as opposed to files
• [x] The file upload endpoint will now return an immediate file_id for each file uploaded (negating the need for the file-status call)
• [x] Large-ish files of at least 10MB should be able to be uploaded.
• [x] Multiple files can be uploaded at a time, the CLI should permit this if possible.

All tests etc. should be revised to reflect this, at the moment the upload should fail given the new API spec.

[bschroeter]

Multiple files can be uploaded at the same time up to the total packet size of 200mb (set on the server)