Refactor into IDE-like panel+editor layout.

[preston]

In v1, the app only supports HL7 CDS KNARTS. v2 will remove this assumption by supporting FHIR Clinical Reasoning Module services via #10 and #11 . Doing so requires changing to a slightly more sophisticated layout. Once FHIR support is available, some navigational panes will be necessary.

I'm envisioning something very similar to the project explorer trees implemented by IDEA, Eclipse, VS Code, Sublime, Atom -- and pretty much everything else -- that is directly integrated with the backend repository (via FHIR calls) when launched in SMART-on-FHIR mode. Assuming this paradigm works out, the current app would essentially become an editor instance for whatever resources you want to open.