Included some improvements and favicons

Hey, I am sending some improvements on the new website :)
- Pep8 and syntax highlighting for sample code;
- Install code on the main page button;
- Buttons on the footer for following, forking or staring our Github project;
- Favicons;

![scrapy org improvements](https://cloud.githubusercontent.com/assets/6334727/4600266/88141bea-50d1-11e4-9964-dbe8945c4039.png)