Install systemd unit file from setup.py

Now distributions created from setup.py put the systemd unit file in the
correct location for units provided by packages.  It may then be enabled
and started by the user with systemctl.

Closes #11.

setup.py

@@ -28,7 +28,8 @@ setup(
     install_requires=["requests"],
     data_files = [
         ("/usr/share/kaylee", ["data/icon_inactive.png", "data/icon.png",
-            "options.json.tmp"])
+            "options.json.tmp"]),
+        ("/usr/lib/systemd/user", ["systemd/kaylee.service"])
     ],
     entry_points = {
         "console_scripts": [