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/src/Shared.elm

@@ -0,0 +1,7 @@
+module Shared exposing (..)
+
+clientOrigin =
+    "http://localhost:8000"
+
+serverOrigin =
+    "http://localhost:3000"