Open a magic-wormhole with the user-supplied code in the FrontendRoute_AcceptFolderInvite route

See obelisk/frontend/src/Controller.hs, pageFromRoute.

The route already retrieves the entered wormhole code in to r.

Instead of just rendering the code into the page, use it to open a wormhole connection and receive the folder invite details. Then, render the invite details into the page (no styling required, just make the functionality work).