add Raspbian template

Hi,

This adds a proper template for Raspbian. (Debian rebuilt for the RaspberryPi)
It's like Debian, but cut down: not 'unstable' respository, only stable & testing; non non-free 'any' packages (only all), not proposed-updates, backports etc... so there is not point to confuse users with thoses.

The packagers currenlty uses one-off brutal search & replace
http://debdiffs.raspbian.org/main/u/unattended-upgrades/