relicensing

Hi all, 

As @fperez asked on last google hangout, this is a request to relicence nbviewer under BSD Licence. By creating it while copy pasting a Bootstrap example I made it under Apache  licence by mistake, and we would like an uniform licence under all IPython projects.

Still I would like the authorization of peoples who contributed, ie
   - @rgbkrk
   - @v923z
   - @minrk
   - @takluyver
   - and Myself (I of course agree) .

Additionally to just relicensing this PR update the footer at the bottom of each page to link to contributor pages, and keep the APACHE license file around  stating that all bootstrap files still stays under apache liscence.

Thanks.