Switch to "standard" android fs layout and make flashing possible with just a b2g checkout (and some patience).

 - /system is now a separate partition
 - the bcm2835 firmware files from upstream raspberrypi are added (the full repo is too large)
 - initial partitioning and flashing scripts, to evolve into
   full-fledged top-level ./flash.sh commands
 - bootanimation.zip updated for currently-restricted output resolution