Load/Save settings

- renamed all settings with dot syntax
- refactored Menu->settings()
- changed schema of settings table to allow longer setting name and value
- added getAll() static method on Setting Model to fetch all settings (with proper unserialize of value)

lib/Settings/Pages.php

@@ -0,0 +1,23 @@
+<?php
+namespace MailPoet\Settings;
+
+class Pages {
+
+  static function getAll() {
+    $mailpoet_pages = get_posts(array(
+      'post_type' => 'mailpoet_page'
+    ));
+
+    $pages = array_merge($mailpoet_pages, get_pages());
+
+    foreach($pages as $key => $page) {
+      $page = (array)$page;
+      $page['preview_url'] = get_permalink($page['ID']);
+      $page['edit_url'] = get_edit_post_link($page['ID']);
+
+      $pages[$key] = $page;
+    }
+
+    return $pages;
+  }
+}