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.preinst

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+# Remove any cached CPython directories or files
+echo "Cleaning up existing CPython files"
+find /usr/share/pvc/pvcworkerd -type d -name "__pycache__" -exec rm -rf {} \; &>/dev/null || true