Strip default items from session snapshots(?)

[cmdcolin]

trafficstars

this could be a large-ish task but session snapshots tend to be kind of bloated with a lot of default values being included. config snapshots specifically have logic to remove these. it uses the fact that config slots have a defaultValue to compare to. with session/view/track/display model snapshots, this logic for removing might be more "bespoke"