feat(users): add myth-auth to handle users crud + add admin gateway only accessible by login

- overwrite myth/auth config with castopod app needs
- create custom views for users authentication
- add admin area bootstrapped by admin controller
- shift podcast and episodes crud to admin area
- reorganize view layouts
- update docs for database migration
- add myth-auth to DEPENDENCIES.md

closes #11

app/Controllers/Admin/BaseController.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace App\Controllers\Admin;
+
+/**
+ * Class BaseController
+ *
+ * BaseController provides a convenient place for loading components
+ * and performing functions that are needed by all your controllers.
+ * Extend this class in any new controllers:
+ *     class Home extends BaseController
+ *
+ * For security be sure to declare any new methods as protected or private.
+ *
+ * @package CodeIgniter
+ */
+
+use CodeIgniter\Controller;
+
+class BaseController extends Controller
+{
+    /**
+     * An array of helpers to be loaded automatically upon
+     * class instantiation. These helpers will be available
+     * to all other controllers that extend BaseController.
+     *
+     * @var array
+     */
+    protected $helpers = ['auth'];
+
+    /**
+     * Constructor.
+     */
+    public function initController(
+        \CodeIgniter\HTTP\RequestInterface $request,
+        \CodeIgniter\HTTP\ResponseInterface $response,
+        \Psr\Log\LoggerInterface $logger
+    ) {
+        // Do Not Edit This Line
+        parent::initController($request, $response, $logger);
+
+        //--------------------------------------------------------------------
+        // Preload any models, libraries, etc, here.
+        //--------------------------------------------------------------------
+        // E.g.:
+        // $this->session = \Config\Services::session();
+    }
+}