Show template name in source code

I think this could be very useful. People keep asking which template has been used to render a specific part of the website so why not just output it in the HTML source code when the debug mode is enabled? ;-)

![bildschirmfoto 2014-04-01 um 13 44 19](https://cloud.githubusercontent.com/assets/481937/2578575/078bdbc8-b993-11e3-9b22-ae8a69a961a1.png)