Implemented WebHooks delivery queue.

Completely removed usage of the RabbitMQ. Queue now based on Redis channels.
Worker process now extracted as separate docker container.
Base image upgraded to the 1.8.0 version (PHP 7.2.7 and pcntl extension).

tests/codeception/common/_support/queue/CodeceptionQueueHelper.php

@@ -14,7 +14,12 @@ class CodeceptionQueueHelper extends Module {
      */
     public function grabLastQueuedJob() {
         $messages = $this->grabQueueJobs();
-        return end($messages);
+        $last = end($messages);
+        if ($last === false) {
+            return null;
+        }
+
+        return $last;
     }
 
     /**