Massive rejigger into single daemon

Completely restructure the daemon code to move the 4 discrete daemons
into a single daemon that can be run on every hypervisor. Introduce the
idea of a static list of "coordinator" nodes which are configured at
install time to run Zookeeper and FRR in router mode, and which are
allowed to take on client network management duties (gateway, DHCP, DNS,
etc.) while also allowing them to run VMs (i.e. no dedicated "router"
nodes required).

debian/pvc-daemon.postinst

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+# Enable the service
+systemctl enable /lib/systemd/system/pvcd.service
+
+if systemctl is-active --quiet pvcd.service; then
+    echo "The PVC node daemon has not been restarted; this is up to the administrator."
+else
+    echo "The PVC node daemon has not been started; create a config file at /etc/pvc/pvcd.conf then start it."
+fi