More Bpmn/Workflow handling layer refactoring and improve unit tests

workflow/engine/src/ProcessMaker/Exception/ProjectNotFound.php

@@ -0,0 +1,20 @@
+<?php
+namespace ProcessMaker\Exception;
+
+use ProcessMaker\Project;
+
+class ProjectNotFound extends \RuntimeException
+{
+    const EXCEPTION_CODE = 20;
+
+    public function __construct(Project\Handler $obj, $uid, $message = "", \Exception $previous = null) {
+        $message = empty($message) ? sprintf("Project \"%s\" with UID: %s, does not exist.", get_class($obj), $uid) : $message;
+
+        parent::__construct($message, self::EXCEPTION_CODE, $previous);
+    }
+
+    public function __toString()
+    {
+        return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
+    }
+}