feat: add guestbook with rate limiting (#6)

* Re-add guestbook w/ rate limiting
* Add guestbook to navbar

app/Http/Controllers/GuestbookController.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use Illuminate\Http\Request;
+use DB;
+
+class GuestbookController extends Controller {
+    public function guestbook() {
+        return view('pages.guestbook');
+    }
+
+    public function guestbookPost(Request $request) {
+        $this->validate($request, [
+            'name' => 'required',
+            'message' => 'required'
+        ]);
+
+        DB::insert('INSERT INTO guestbook_entries (name, timestamp, ip_address, agent, message) values (?, ?, ?, ?, ?)', array(
+            htmlspecialchars($request->get('name')),
+            time(),
+            $request->ip(),
+            $request->userAgent(),
+            htmlspecialchars($request->get('message'))
+        ));
+
+        return back()->with('success', 'Entry submitted successfully!');
+    }
+}