bugfix: don't use JsonConvert, create a serializer
bugfix: don't use JsonConvert, create a serializer

JsonConvert falls back to JsonConvert.DefaultSettings, which makes it
hard to have deterministic behavior. We want a consistent json format
regardless of what the hosting app sets the default settings to.

NFig/NFig.UI,NFig/NFig.UI,NFig/NFig.UI,NFig/NFig.UI