Move stateful around

/mnt/stateful_partition was already a little unruly with
/mnt/stateful_partition/home and /mnt/stateful_partition/var_overlay
serving similar functional purposes.

Then we needed to also add /opt and /srv overlays.

I also have wanted to get rid of the ugly and weird
/mnt/stateful_partition name so lets just have one big move. :worried: 

/mnt/stateful_partition -> /media/state
/mnt/stateful_partition/var_overlay -> /media/overlays/var
/mnt/stateful_partition/home -> /media/overlays/home

From there we add /media/overlays/srv and /media/overlays/opt