persistence-ready (testing only!) build info (#75)

if PERSISTENCE=1, the image will have a  subsequent encrypted partition.
This is ONLY for testing. Really, using it on real scenarios is a _complete_ security failure.
Please don't do it.

/etc/freepto is replacing /etc/freepto_version, allowing us to automatically embed build information inside
the image.
gigolo integrates with thunar avana-bbs#87
Haveged for fast /dev/random; closes avana-bbs#133