grade.py: Less dependencies on defaultParams.json
grade.py: Less dependencies on defaultParams.json

We use default values for variables not defined in defaultParams.json

France-ioi/taskgrader,France-ioi/taskgrader,France-ioi/taskgrader,France-ioi/taskgrader,France-ioi/taskgrader,France-ioi/taskgrader,France-ioi/taskgrader