Make spaceranger process optional

[allyhawkins]

Because the spaceranger step is very costly and takes a long time to run, we should incorporate the option to skip this step (similar to how we skip the production of the rad file in alevin-fry). In doing this, we should break out the file reorganization into it's own process so the first process is running spaceranger and the second process is file re-organization and creating the metadata.json.

[jaclyn-taroni]

My suspicion is that GitHub was having issues when #134 went in. Closing this!