Services toggle script

[aw]

Related to on-prem/jidoteki-admin-api#11

The services toggle script update_services.sh should generate entries for the services.json as well as generate services flag files to be read by the boot script.

For forward compatibility, the list of services which can be toggled should be stored in a simple text configuration file.

Upon running the script and updating services.json, the script should then attempt to start the services whose toggle files are present, and attempt to stop the services whose toggle files are missing 😕

EDIT: changed the order, present toggle files = start, missing = stop

[aw]

Note: Ensure https://github.com/unscramble/jidoteki-admin/blob/master/roles/admin/templates/update_settings.sh.j2 also moves services.json