Run systemd service as scream user

Add scripts to configure additional user scream for systemd service

Receivers/unix/debian/scream.postinst

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+useradd \
+	--no-user-group \
+	--create-home \
+	--home-dir /var/lib/scream \
+	--shell /usr/sbin/nologin \
+	--groups audio \
+	--system \
+	scream
+
+# Enable and start the service
+systemctl disable scream.service
+
+# Explicitly exit 0
+exit 0

Receivers/unix/debian/scream.prerm

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+# Disable and stop the service
+systemctl disable --now scream.service
+
+# Remove the user
+userdel scream
+
+# Clean up the data directory (don't worry about program files, 'dpkg' handles that!)
+rm -rf /var/lib/scream
+
+# Explicitly exit 0
+exit 0

Receivers/unix/debian/scream.service

@@ -3,6 +3,7 @@ Description=Scream audio receiver
 After=sound.target
 
 [Service]
+User=scream
 ExecStart=/usr/bin/scream -o alsa
 ExecReload=/bin/pkill scream
 RestartSec=5