Add systemd service unit file and D-Bus config

The unit file is only for debugging purposes.
The Makefile is used to install (link --runtime), start, stop, and
restart the service, and to see the output (journalctl)

sfsmcd/org.ddnss.sfs.mc.conf

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
+    "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
+<busconfig>
+    <policy user="root">
+        <allow own="org.ddnss.sfs.mc"/>
+    </policy>
+
+    <policy context="default">
+        <allow send_destination="org.ddnss.sfs.mc"/>
+    </policy>
+</busconfig>

sfsmcd/sfsmc-debug@.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=SFS Minecraft server (Debug)
+After=network.target
+
+[Service]
+Type=dbus
+BusName=org.ddnss.sfs.mc
+ExecStart=%I/sfs-mc/target/debug/sfsmcd
+User=root