Port TurnKey Linux to RaspberryPi (and potentially other ARM based arch/hardware)

[JedMeister]

It'd be super awesome if users could simply download TurnKey Linux and "burn" it straight to an SD card and then it would "just work" ™️ on their RaspberryPi! 😄

To close this issue we will need to achieve the following:

• port/fork TurnKey bootstrap so it can produce a Raspbian based TurnKey bootstrap
• port/fork TurnKey buildroot so we can build Raspbian packages for inclusion in the TurnKey apps
• a new TKLDev based appliance (amd64 build) to support building any Raspbian based TurnKey app (will probably want to include pool and chanko as per TKLDev should support building Debian packages from source #231 - then Raspian ports of our custom software can be built at build time)
  • I assume that it will probably be necessary to include QEMU into this TKLDev-RPiBuilder app (as per [TKLDev] Include QEMU so as to allow cross compiling of alternative architechures #265 - otherwise how else would you be able to build in a non-native chroot??)
• Once the above is complete the anyone should be able to build this special version of TKLDev (in an existing amd64 TKLDev). Then launch that and output something like turnkey-core-14.1-jessie-rpi.img (or similar). This .img file could then be written direct to an SD card (e.g. via dd) and the RaspberryPi should boot straight up!

Note I suggest that we use rpi as the ARCH type to denote a Raspbian based build. That will avoid confusion if in the future we create a more generic Debian based armhf ARCH build.