Scaffold a demo app which integrates with the Holo-REA backend

Once we have a component to test (see #2), we should integrate it with a real backend. At this stage my gut feeling is that it makes sense to develop the actual app within the Holo-REA codebase, in the examples folder.

• set up Sapper to serve the site
• bring in vf-graphql-holochain and svelte-apollo to get GraphQL integrated (the former module should be set up through the project's Yarn workspace, not loaded via NPM)