- Updates Migrator with new column for Segments

- Updates Segmnets tests
- Updates MailPoet's Notice.js with additional options
- Updates Import's router, WP menu bootstrap logic, client- and
  server-side logic

lib/Router/Import.php

@@ -2,6 +2,8 @@
 namespace MailPoet\Router;
 
 use MailPoet\Import\MailChimp;
+use MailPoet\Models\CustomField;
+use MailPoet\Models\Segment;
 
 if(!defined('ABSPATH')) exit;
 
@@ -15,4 +17,40 @@ class Import {
     $mailChimp = new MailChimp($data['api_key'], $data['lists']);
     wp_send_json($mailChimp->getSubscribers());
   }
-}
+
+  function addSegment($data) {
+    $segment = Segment::createOrUpdate($data, $returnObject = true);
+    wp_send_json(
+      (!is_array($segment)) ?
+        array(
+          'status' => 'error',
+          'message' => $segment
+        ) :
+        array(
+          'status' => 'success',
+          'segment' => $segment
+        )
+    );
+  }
+
+  function addCustomField($data) {
+    $customField = CustomField::create();
+    $customField->hydrate($data);
+    $result = $customField->save();
+    wp_send_json(
+      (!$result) ?
+        array(
+          'status' => 'error'
+        ) :
+        array(
+          'status' => 'success',
+          'customField' => $customField->asArray()
+        )
+    );
+  }
+
+  function process($data) {
+    $import = new \MailPoet\Import\Import(json_decode($data, true));
+    wp_send_json($import->process());
+  }
+}