Create system-wide systemd service for turning rplidar off and pinging pimu

[hello-binit]

The hello_robot_lrf_off.desktop and hello_robot_pimu_ping.desktop are autostarted by systemd whenever the user signs in. However, if the user disabled auto sign in (e.g. because they created multiple users), the robot's rplidar won't stop spinning / the pimu won't be pinged, until the user signs in. SSH-ing into the robot doesn't count as signing in; it has to be done through the GUI. Since we want the both of these things to happen when the robot boots, let's make them system-wide systemd services that trigger when the system is up.