React dev server for real time UI updates in development

[samcraftt]

Currently, when running the client locally, the electron client serves from a static, production build of the frontend React server. This implements a slight change to setting up the local environment:

• dev.sh starts the React server separately before starting the Electron client (with a headless browser), which is reachable at http://localhost:3000
• dev.sh starts the electron client, setting the ENVIRONMENT env variable to "development" to indicate that the electron client should serve from the React dev server available at http://localhost:3000, not the static build files

This has the effect of, for example, if I were to change the button text from "Visualize" to "Visualize this dataset", and save the file, the electron client UI will auto recompile and update. Makes UI dev easier, we don't have to rebuild and rerun every time we want to see the results of any frontend client change.

@akgohain I removed an webpack override in client/package.json to do this... which was probably there for good reason. let me know if I need to put this back.