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
- All HostMetadata information becomes NodeMetadata
- Significant change to mechanics, but same net effect
- LocalNets becomes "local_networks", space-separated list of CIDRs
- Load becomes simple single string
- Use MakeHostNodeID for indexing into Host topology
- (That changes the app /origin/{id} handler; will be removed later)
