Add setup script for linux

Installer/setup.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+set -eu
+
+if [ "$(id -u)" -ne 0 ]; then
+    echo 'root privileges required' >&2
+    exit 1
+fi
+
+copy_sl_config() {
+	if [ -e "/opt/itgmania/Themes/Simply Love.old/$1" ]; then
+		cp "/opt/itgmania/Themes/Simply Love.old/$1" "/opt/itgmania/Themes/Simply Love/$1"
+	fi
+}
+
+cd "$(dirname "$0")"
+
+# Move the old SL release out of the way
+[ -d /opt/itgmania/Themes/Simply\ Love ] && mv /opt/itgmania/Themes/Simply\ Love{,.old}
+
+# Install ITGm
+[ -d /opt ] || install -d -m 755 -o root -g root /opt
+cp -R --preserve=mode,timestamps itgmania /opt
+ln -sf /opt/itgmania/itgmania.desktop /usr/share/applications
+
+# Copy persistent files over from the old SL folder
+if [ -d /opt/itgmania/Themes/Simply\ Love.old ]; then
+	copy_sl_config Other/SongManager\ PreferredCourses.txt
+	copy_sl_config Other/SongManager\ PreferredSongs.txt
+
+	rm -rf /opt/itgmania/Themes/Simply\ Love.old
+fi