Bug#819664: Re-organise the CD / download pages to make them more useful

Hi,

some texts which should be considered:

> * Verify your download

https://www.debian.org/CD/verify
https://www.debian.org/CD/faq/#verify

> * How to write to USB 

https://www.debian.org/CD/faq/#write-usb

> * How to write to optical media

https://www.debian.org/CD/faq/#record-unix
https://www.debian.org/CD/faq/#record-windows
https://www.debian.org/CD/faq/#record-mac

The overhaul should already prepare for the announced demise
of MD5 and SHA1.


Have a nice day :)

Thomas