Support standalone SMART on FHIR launch

[zeevo]

Is your feature request related to a problem? Please describe.
The starter currently supports an EHR launch by default. It should be configurable to support a standalone launch.

Describe the solution you'd like
By configuring smart.js, I should be able to select "standalone" as my launch config. And webpack should build the app appropriately.

[friccita]

Has this issue been resolved? I have been trying to test this and have not been able to get index.html to insert and render the React components after successfully configuring and logging in as a test patient; it just shows a blank page. (In the Cerner code sandbox, my app is registered, but I see no "Begin Testing" option -- I can only click on the app to edit settings or delete it, but not test it, so I'm not sure how to launch from the Cerner sandbox.)