auto restore last attempt training

![screen shot 2014-09-07 at 22 55 35](https://cloud.githubusercontent.com/assets/4983239/4178625/2f710756-369f-11e4-837b-8bb14d17017b.png)

1. If a student haven't done a coding question, his code will be saved and auto restore next time.

2.provide a button if he wants to revert to the template code

3.UI is not beautiful.. need improve
we can render multiple <textarea name="ans" id="ans" render="code" ... /> we can provide mulitple prefilled if needed, but your code will break if we do so.