refactor(auth): change contributor's role logic to have it included in the users_podcasts table

- update myth-auth and codeigniter to latest develop changes
- improve permission check: remove all
dynamic permissions per podcast and overwrite myth-auth services and permission filter
- remove
unnecessary code because of myth-auth upgrade
- refactor some controller code for better clarity
-
add remaining seeders in docs

closes #19, #20

app/Authorization/GroupModel.php

@@ -0,0 +1,18 @@
+<?php namespace App\Authorization;
+
+class GroupModel extends \Myth\Auth\Authorization\GroupModel
+{
+    public function getContributorRoles()
+    {
+        return $this->select('auth_groups.*')
+            ->like('name', 'podcast_', 'after')
+            ->findAll();
+    }
+
+    public function getUserRoles()
+    {
+        return $this->select('auth_groups.*')
+            ->notLike('name', 'podcast_', 'after')
+            ->findAll();
+    }
+}