adding planet.ros.org feed to wiki sidebar

It looks like this at the moment. It could use a litle tlc on the formatting. My javascript/html foo is still very rudimentary. In particular I'd like to have it in a bulleted list not a set of divs. 

![image](https://cloud.githubusercontent.com/assets/447804/4489671/ae7ce0be-4a1e-11e4-9b0e-894d83498c52.png)

I've tested this on the server but left it on master pending review. 

Another improvement would be to have shippets of the content, maybe a line or two in the preview.