complete area preview

complete area preview by add cascaded selector
Merge branch 'master' into Jack/AddAreaQuestion

Conflicts:
	js/controller/question.preview.js
fix conflict
Merge branch 'Jack/AddAreaQuestion' of https://github.com/charleschu/mvc_survey into Jack/AddAreaQuestion
Merge pull request #20 from charleschu/Jack/AddAreaQuestion

WIP:complete area preview