Support a basic client-side login flow

I will need to remove some of the baggage like:

- Scrub any copy about restaurants
- delete Restaurant.elm
- Change Owner.elm -> Manager.elm

client/shell.nix

@@ -2,6 +2,7 @@ let
   pkgs = import <nixpkgs> {};
 in pkgs.mkShell {
   buildInputs = with pkgs; [
+    nodejs
     elmPackages.elm
     elmPackages.elm-format
     elmPackages.elm-live