fix(routerId): persist routerId across sessions

fix #161

lib/reducers/create-otp-reducer.js

@@ -119,6 +119,16 @@ export function getInitialState (userDefinedConfig, initialQuery) {
   if (config.locations) {
     locations.push(...config.locations.map(l => ({ ...l, type: 'suggested' })))
   }
+  // Check for alternative routerId in session storage. This is generally used
+  // for testing single GTFS feed OTP graphs that are deployed to feed-specific
+  // routers (e.g., https://otp.server.com/otp/routers/non_default_router).
+  // This routerId session value is initially set by visiting otp-rr
+  // with the path /start/:latLonZoomRouter, which dispatches the SET_ROUTER_ID
+  // action and stores the value in sessionStorage.
+  const routerId = window.sessionStorage.getItem('routerId')
+  if (routerId) {
+    config.api.path = `/otp/routers/${routerId}`
+  }
   let queryModes = currentQuery.mode.split(',')
 
   // If 'TRANSIT' is included in the mode list, replace it with individual modes
@@ -541,6 +551,9 @@ function createOtpReducer (config, initialQuery) {
         })
       case 'SET_ROUTER_ID':
         const routerId = action.payload || 'default'
+        // Store routerId in session storage (persists through page reloads but
+        // not when a new tab/window is opened).
+        window.sessionStorage.setItem('routerId', routerId)
         return update(state, {
           config: {
             api: {