Move subtask forecast to a plugin

Plugin repo: https://github.com/kanboard/plugin-subtask-forecast

tests/units/Core/Plugin/HookTest.php

@@ -0,0 +1,62 @@
+<?php
+
+require_once __DIR__.'/../../Base.php';
+
+use Core\Plugin\Hook;
+
+class HookTest extends Base
+{
+    public function testGetListeners()
+    {
+        $h = new Hook;
+        $this->assertEmpty($h->getListeners('myhook'));
+
+        $h->on('myhook', 'A');
+        $h->on('myhook', 'B');
+
+        $this->assertEquals(array('A', 'B'), $h->getListeners('myhook'));
+    }
+
+    public function testMergeWithNoBinding()
+    {
+        $h = new Hook;
+        $values = array('A', 'B');
+
+        $result = $h->merge('myhook', $values, array('p' => 'c'));
+        $this->assertEquals($values, $result);
+    }
+
+    public function testMergeWithBindings()
+    {
+        $h = new Hook;
+        $values = array('A', 'B');
+        $expected = array('A', 'B', 'c', 'D');
+
+        $h->on('myhook', function($p) {
+            return array($p);
+        });
+
+        $h->on('myhook', function() {
+            return array('D');
+        });
+
+        $result = $h->merge('myhook', $values, array('p' => 'c'));
+        $this->assertEquals($expected, $result);
+        $this->assertEquals($expected, $values);
+    }
+
+    public function testMergeWithBindingButReturningBadData()
+    {
+        $h = new Hook;
+        $values = array('A', 'B');
+        $expected = array('A', 'B');
+
+        $h->on('myhook', function() {
+            return 'string';
+        });
+
+        $result = $h->merge('myhook', $values);
+        $this->assertEquals($expected, $result);
+        $this->assertEquals($expected, $values);
+    }
+}