[SPARK-4984][Core][UI] Adding a pop-up containing the full for job description when it is very long

In some case the job description will be very long, such as a long sql. refer to #3718
This PR add a pop-up for job description when it is long. 
![image](https://cloud.githubusercontent.com/assets/7018048/5566579/2f45fb7a-8f68-11e4-87b2-a014269afaff.png)