Add daytimeoverlay/nighttimeoverlay

[EricClaeys]

• These fields are not editable by the user in the WebUI - they are changed in the Overlay Editor but are stored in the settings file.
• install.sh adds the settings to all settings files with a value of "" if not already there.
• Needed to add a "settingsonly" field to the options.json file that tells the WebUI not to display the setting but make sure it's in the settings file.
• Also needed to put the "display" and "settingsonly" fields as the 2nd and 3rd fields in the options file (if specified) so all the other fields except "type" can be ignored.

[EricClaeys]

Alex, please review this PR that adds the daytimeoverlay and nighttimeoverlay fields. If they aren't in the prior settings file, install.sh adds them with a "" value.