Fix Exporting portable projects with QEMU includes base images even when selecting no.

Fix https://github.com/GNS3/gns3-gui/issues/1409

gns3server/handlers/api/project_handler.py

@@ -368,7 +368,8 @@ class ProjectHandler:
         response.content_length = None
         response.start(request)
 
-        for data in project.export(include_images=bool(request.GET.get("include_images", "0"))):
+        include_images = bool(int(request.json.get("include_images", "0")))
+        for data in project.export(include_images=include_images):
             response.write(data)
             yield from response.drain()