Add export for one Biblio entity.

#127 
Adding export for one Biblio entity by adding an extra field using hook_field_extra_fields() and biblio.controller.inc buildContent().

![export3](https://f.cloud.github.com/assets/99186/1829476/d8837200-72c0-11e3-8668-506cee767b55.png)
![export4](https://f.cloud.github.com/assets/99186/1829477/dad92c66-72c0-11e3-922d-ba17e961e552.png)
![selection_011](https://f.cloud.github.com/assets/99186/1830197/d1f698a8-732a-11e3-9670-d044a9bb225d.png)
![selection_009](https://f.cloud.github.com/assets/99186/1830198/d4fd1d10-732a-11e3-8f31-47824379d0e3.png)
![selection_010](https://f.cloud.github.com/assets/99186/1830199/e5f6cd78-732a-11e3-9e8b-bfae7daaccef.png)