ZEPPELIN-164 Paragraph title

Paragraph title 
https://zeppelin-project.atlassian.net/browse/ZEPPELIN-164

![image](https://cloud.githubusercontent.com/assets/1540981/4361460/62376374-4284-11e4-87a2-353bacd49bf0.png)

Like code editor, user can control title show/hide.

Ready to be merged.