Adding assembly to export eclipse package (blank project)

Closes #449 

With this change, we can provide a zip to import as Maven project, and another zip with all dependencies to use only in Eclipse. This second package can help to introduce VRaptor to newbie users.

The new assembly file generates a file structure used by Eclipse.
![screenshot from 2014-06-29 20 39 01](https://cloud.githubusercontent.com/assets/140387/3424817/b2606ca4-ffe7-11e3-8107-ca567a0fd34c.png)