switched LaunchDaemon to Program string

[mpanighetti]

• switched LaunchDaemon from ProgramArguments array to Program string #91
• moved bailout logic to bail_out function to speed up error exits
• removed unused helper script and LaunchDaemon references
• added LaunchDaemon load output to stdout in postinstall
• moved update list-formatting into format_update_list function to allow running software update checks separately from formatting the output
  • formatted update list is now written to plist for later reference and reuse (not yet implemented)
• renamed exit_without_updating to exit_script
  • function is called if there are no recommended updates or if there are no updates at all, with separate stdout messages for each case
• replaced clean_up run at end of install_updates with check_for_updates run (which runs exit_script/clean_up if no updates are found)