Create/Modify/Delete Units individually through API

Responses served to the client needs to be at the granularity that they mean something. Modifying & deleting units as big chunks without a more complex error response was not granular enough. This approach makes it obvious what has happened in response to a request and gives the client the ability to control the behavior on failure quite easily.

This is leaving the door wide open for batch requests in the future.
Right. 404 feels weird, since the user could be trying to create it. 409 feels better, as it's a user-triggered error that can be corrected (by providing fileContents). Thoughts?