[discover/tableRow] iterate on the style of the source field a bit

This is an attempt to improve the style of the _source field in discover. it:
 - removes the natural whitespace around the terms
 - uses the definition list elements
 - extract the addWordBreaks util
 - add work breaks to values in the source, where needed
 - switch from htmlEscape to [_.escape](https://lodash.com/docs#escape)

Before:
![image](https://cloud.githubusercontent.com/assets/1329312/5132546/e7b1672a-70ba-11e4-82ac-2961007f14c7.png)

After:
![image](https://cloud.githubusercontent.com/assets/1329312/5132540/d6e66abc-70ba-11e4-953a-f826b82f491b.png)