Project: stylus
Task (easy): Add 'Save' button (class 'save') and 'Preview' button (class 'preview') in 'common/SurveyDesign.js'. Click 'Save' button to save Survey data to 'localStorage.data'. Survey data format is like `{title:'survey title', questions:[{className:'Question', title:'title 1', name:'question1'}, {className:'Question', title:'title2', name:'question2'}]}`. Each type of question's JSON data should contain all properties from constructor params and configs. Click 'Preview' button to save Survey data and open preview page in new window. Save codes to 'common/SurveyDesign.js'.