Support for source maps in coverage reports

/cc @SevInf @arikon 
Здесь тоже всё грустно

![2014-10-13 19-43-54 common blocks_button_button css html](https://cloud.githubusercontent.com/assets/75247/4616057/c6e731a2-52ef-11e4-953a-bbbc5b0f3cff.png)