Allow stages to supply JSON formatting hints

[coldino]

Currently there's a hard-coded list of field sets that should be shorted onto a single line present in automate/jsonutils.py. This code should not have that knowledge.

• [ ] Extend jsonutils to accept a list of field sets during encoding
• [ ] Extend the export stage system, allowing stages to optionally provide a list of field sets

Given Python's regex system caches all regex string compilations there's probably no need to be clever with this.