chore(06-02): download and include Action Scheduler library

- Downloaded Action Scheduler 3.9.3 from GitHub
- Placed in vendor/action-scheduler/ directory
- Included in main plugin file before other code for proper initialization
- Library will auto-initialize itself when required

vendor/action-scheduler/lib/cron-expression/CronExpression_YearField.php

@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * Year field.  Allows: * , / -
+ *
+ * @author Michael Dowling <mtdowling@gmail.com>
+ */
+class CronExpression_YearField extends CronExpression_AbstractField
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function isSatisfiedBy(DateTime $date, $value)
+    {
+        return $this->isSatisfied($date->format('Y'), $value);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function increment(DateTime $date, $invert = false)
+    {
+        if ($invert) {
+            $date->modify('-1 year');
+            $date->setDate($date->format('Y'), 12, 31);
+            $date->setTime(23, 59, 0);
+        } else {
+            $date->modify('+1 year');
+            $date->setDate($date->format('Y'), 1, 1);
+            $date->setTime(0, 0, 0);
+        }
+
+        return $this;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function validate($value)
+    {
+        return (bool) preg_match('/[\*,\/\-0-9]+/', $value);
+    }
+}