Add 'Bounced' status to subscribers [MAILPOET-684]

Fix SubscriberTest->testItHasGroupFilter() making only one of four assertions due to lack of data.
Fix a small issue with Import. Unexpected values for the status field were converted to 'unconfirmed' rather than 'subscribed' due to non-strict comparison in in_array(). This hindered 'bounced' status import as well.

lib/Models/Subscriber.php

@@ -13,6 +13,7 @@ class Subscriber extends Model {
   const STATUS_SUBSCRIBED = 'subscribed';
   const STATUS_UNSUBSCRIBED = 'unsubscribed';
   const STATUS_UNCONFIRMED = 'unconfirmed';
+  const STATUS_BOUNCED = 'bounced';
 
   const SUBSCRIPTION_LIMIT_COOLDOWN = 60;
 
@@ -335,6 +336,11 @@ class Subscriber extends Model {
         'label' => __('Unsubscribed', 'mailpoet'),
         'count' => self::filter(self::STATUS_UNSUBSCRIBED)->count()
       ),
+      array(
+        'name' => self::STATUS_BOUNCED,
+        'label' => __('Bounced', 'mailpoet'),
+        'count' => self::filter(self::STATUS_BOUNCED)->count()
+      ),
       array(
         'name' => 'trash',
         'label' => __('Trash', 'mailpoet'),
@@ -720,6 +726,12 @@ class Subscriber extends Model {
       ->where('status', self::STATUS_UNCONFIRMED);
   }
 
+  static function bounced($orm) {
+    return $orm
+      ->whereNull('deleted_at')
+      ->where('status', self::STATUS_BOUNCED);
+  }
+
   static function withoutSegments($orm) {
     return $orm->select(MP_SUBSCRIBERS_TABLE.'.*')
       ->leftOuterJoin(