docker: images optimisation: - reduced the number of layers by grouping many instructions - moved stuff which don't change a lot at the beginning, and hg/apt at the end - scripts are not now in scripts/ subdirectories - prosody.cfg.lua is added using ADD instead of getting it online - .hg/dirstate is copied in base (backend) and libervia, so mercurial revision is known - removed lot of useless WORKDIR instruction, they are replaced by "cd" inside RUN instructions - cleaning (apt-clean, rm) is done on the same instruction as the one than generate the data, to avoid useless data in layers

$ORIGIN <domain>.
$TTL 1D
@     IN SOA   <hostname> <hostname> (
                        <date>    ; serial
                        8H        ; refresh
                        4H        ; retry
                        4W        ; expire
                        1D )      ; minimum

                NS      <hostname>
www             CNAME   <hostname>
localhost       A       127.0.0.1
<hostname>      A       127.0.0.1

_xmpp-client._tcp.<domain>. 18000 IN SRV 0 5 <c2s_port> <hostname>.<domain>.
_xmpp-server._tcp.<domain>. 18000 IN SRV 0 5 5269       <hostname>.<domain>.