Add a systemd service file for starting Kaylee

Next I need to make the setup.py script install it.  It's meant to be a
user service (installed to /usr/lib/systemd/user/), since Kaylee
currently does not support being run outside of a normal user account.

Also, it would be really nice to make it possible to reload the service
once it has been started.  This will require some changes to Kaylee to
support synchronously reloading configuration.  I understand that you
aren't supposed to reload units asynchronously, and I *really* can't
trust Kaylee to reload succinctly since reloading configuration may
require contacting a remote server until #10 is implemented.
Configuration reloading may be a separate issue from the systemd unit
file, but I'd like to see it by version 0.2.

systemd/kaylee.service

@@ -0,0 +1,8 @@
+[Unit]
+Description=Somewhat fancy voice command recognition software
+
+[Service]
+ExecStart=/usr/bin/kaylee
+
+[Install]
+WantedBy=default.target