Optional stylesheet link that can be used for improve the macros' displa...

Basically I added an optional stylesheet link into the grid prevalues that can be used to improve the macros' display into the grid. This way, the editor can have a nicer preview of the macro and its content.
![capture2](https://cloud.githubusercontent.com/assets/1587387/4865328/448de484-6123-11e4-8d4d-33fe594bed4a.PNG)
![capture](https://cloud.githubusercontent.com/assets/1587387/4865335/51de46f6-6123-11e4-9a7e-0d83c1be68a0.PNG)