enhanced plugin support (#634)

- refactored admin controller and templates
- plugin support for entity actions
- changed column mail to email in customer table
- refactored theme events

src/Timesheet/Util.php

@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Timesheet;
+
+/**
+ * A static helper class for re-usable functionality.
+ */
+class Util
+{
+    /**
+     * Calculates the rate for a hourly rate and a given duration in seconds.
+     *
+     * @param float $hourlyRate
+     * @param int $seconds
+     * @return float
+     */
+    public static function calculateRate(float $hourlyRate, int $seconds): float
+    {
+        $rate = (float) ($hourlyRate * ($seconds / 3600));
+        $rate = round($rate, 2);
+
+        return $rate;
+    }
+}