Improve email sending system and add Postmark as mail transport

app/Core/EmailClient.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace Core;
+
+/**
+ * Mail client
+ *
+ * @package  core
+ * @author   Frederic Guillot
+ */
+class EmailClient extends Base
+{
+    /**
+     * Send a HTML email
+     *
+     * @access public
+     * @param  string  $email
+     * @param  string  $name
+     * @param  string  $subject
+     * @param  string  $html
+     */
+    public function send($email, $name, $subject, $html)
+    {
+        $this->container['logger']->debug('Sending email to '.$email.' ('.MAIL_TRANSPORT.')');
+
+        $start_time = microtime(true);
+        $author = 'Kanboard';
+
+        if (Session::isOpen() && $this->userSession->isLogged()) {
+            $author = e('%s via Kanboard', $this->user->getFullname($this->session['user']));
+        }
+
+        switch (MAIL_TRANSPORT) {
+            case 'postmark':
+                $this->postmark->sendEmail($email, $name, $subject, $html, $author);
+                break;
+            default:
+                $this->smtp->sendEmail($email, $name, $subject, $html, $author);
+        }
+
+        $this->container['logger']->debug('Email sent in '.round(microtime(true) - $start_time, 6).' seconds');
+    }
+}