Switched to sphinx design tabs because sphinx tabs are not supported with pydata theme.

- Specify language for codeblocks to fix build warnings

Signed-off-by: Ayush Singh <ayushdevel1325@gmail.com>

* All of the subsequent headers are at the wrong level. Fix by simply
  removing the first header which is superfluous anyway.

Changed from bone-cook-book to beaglebone-cookbook

Updated images, links and code.