SystemServer: Read service list from a config file

This replaces the hardcoded services list with a very simple config
file in /etc/SystemServer.ini :^)

Closes https://github.com/SerenityOS/serenity/issues/610

Base/etc/SystemServer.ini

@@ -0,0 +1,28 @@
+[TTYServer]
+# NOTE: We don't start anything on tty0 since that's the "active" TTY while WindowServer is up.
+Arguments=tty1
+StdIO=/dev/tty1
+Priority=high
+
+[ProtocolServer]
+Priority=low
+User=anon
+
+[LookupServer]
+Priority=low
+User=anon
+
+[WindowServer]
+Priority=high
+User=anon
+
+[AudioServer]
+Priority=high
+User=anon
+
+[Taskbar]
+Priority=high
+User=anon
+
+[Terminal]
+User=anon