(add template and routing for message attendees form)

app/Http/Controllers/Backstage/ConcertMessagesController.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace App\Http\Controllers\Backstage;
+
+use Illuminate\Http\Request;
+use App\Http\Controllers\Controller;
+use Illuminate\Support\Facades\Auth;
+
+class ConcertMessagesController extends Controller
+{
+    public function create($id)
+    {
+        $concert = Auth::user()->concerts()->findOrFail($id);
+
+        return view('backstage.concert-messages.new', ['concert' => $concert]);
+    }
+}