Adding a basic mechanism to choose overlays (not operational yet)

src/lib/ids.ts

@@ -27,6 +27,7 @@ const coding = {
 const routes = {
   dbdef: route('dbdef', coding),
   state: route('state', coding),
+  overlays: route('overlays', coding),
   account: route('account/:account', coding),
   settings: route('settings', coding),
   gpx: route('gpx/:gpx', coding),