rename task to project_task and task_user to project_task_user; create project_task_category, fix bug in create project method

backend/modules/task/models/ProjectTaskCategory.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace backend\modules\task\models;
+
+
+class ProjectTaskCategory extends \common\models\ProjectTaskCategory
+{
+
+}