Setup basic REST API backend & Angular proxy for said backend

Once the intial project structure has been merged into master we have a frontend and backend running which can only serve the Angular application.
It would be nice if there was a basic API endpoint setup for the frontend example to talk to.
This could just be a json object response that the frontend can display on a simple page.

On the Angular side it would also be nice to have a development server proxy setup ([just like the FF Console has](https://github.com/frankframework/frankframework/blob/master/console/frontend/src/main/frontend/src/proxy.conf.json)) so development with Angular will immediately be responsive to frontend changes while being to communicate with the backend.