Automatically attach uploaded files to model output

[bschroeter]

Due to the way the API is designed, a file must first be uploaded, then attached to a model output in 2 discrete calls.

We implement this with the methods/CLI:

1. upload_files (or some variant thereof)
2. attach_files_to_model_output

This will become tedious once scripted in conjunction with benchcab.

I suggest we add optional arguments to the upload routines to specify a model output that does little more than issue the attach command immediately after the upload.

I'm in discussions with UNSW as to the ramifications of this approach.

[bschroeter]

Initial implementation, waiting on #42 to incorporate changes across all upload options.