Handle height/width in CommonViewer.

Closes #59 

### Example js533sk1281
![height-width](https://cloud.githubusercontent.com/assets/96776/4686875/41bebbf8-564b-11e4-9f77-cf087e2c87bd.gif)

This assumes we will only have 2 rows max in the header.  We may need to do something different here if we're going to have a more dynamic header.