Port all Celery worker functions to discrete pkg

Moves all tasks run by the Celery worker into a discrete package/module
for easier installation. Also adjusts several parameters throughout to
accomplish this.

debian/pvc-daemon-worker.postinst

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+# Reload systemd's view of the units
+systemctl daemon-reload
+
+# Enable the service and target
+systemctl enable /lib/systemd/system/pvcworkerd.service
+
+# Inform administrator of the service restart/startup not occurring automatically
+if systemctl is-active --quiet pvcworkerd.service; then
+    echo "NOTE: The PVC worker daemon (pvcworkerd.service) has not been restarted; this is up to the administrator."
+else
+    echo "NOTE: The PVC worker daemon (pvcworkerd.service) has not been started; create a config file at /etc/pvc/pvc.conf then start it."
+fi