When the scope-app restarts, it no longer has a
reference to the previous node set. Therefore,
the delta update adds *all* nodes but does not
remove legacy ones.
`reset==true` tells the frontend to start fresh.
Fixes#2708
Squash of:
- use detailed.Summaries to render topology nodes
- ban merging nodes of different topologies (they should be mapped)
- need to prune parents when mapping node types
- render container images by id if they have no name
- remove separate render ids and prune parents in NewDerived*
- don't render metrics/metadata for groups of nodes
- fixing up tests
- removing pending unit tests (for mapping.go, for now)
- updating experimental dir for RenderableNode removal
