ProcessMaker-MA "Process Variables (fixes & behat)"

- Se han agregado validaciones faltantes
- Se han implementado los siguientes features (behat):
    GET /api/1.0/{workspace}/project/{prj_uid}/variables
    GET /api/1.0/{workspace}/project/{prj_uid}/grid/variables
    GET /api/1.0/{workspace}/project/{prj_uid}/grid/{grid_uid}/variables

workflow/engine/src/BusinessModel/Process.php

@@ -1569,6 +1569,7 @@ class Process
                     $dynaForm = new \BusinessModel\DynaForm();
 
                     $dynaForm->throwExceptionIfNotExistsDynaForm($gridUid, $processUid, $this->arrayFieldNameForException["gridUid"]);
+                    $dynaForm->throwExceptionIfNotIsGridDynaForm($gridUid, $this->arrayFieldNameForException["gridUid"]);
 
                     //Get data
                     $file = PATH_DYNAFORM . $processUid . PATH_SEP . $gridUid . ".xml";