Re #1086 basic time schedule check for watches

[dgtlmoon]

Closes #1086
Todo

• Validate that 'from' value is less than 'until' (but actually a null value on either is ok)
• Hook update to set defaults for existing watches (all days on, 00-24 etc) if needed (maybe if 'None' then enable all anyway, on that save it should set the right values, and if 'None' in the loop then assume "OK")
• How does this play with API updated?
• Add a much more obvious 'Use default interval and schedule' checkbox
• Add some function to the Watch model like is_schedule_permitted and hook into the Queue loop
• configurable timezone (add option "Use system timezone")
• make timezone apply at app start (or use system timezone)

If system TZ is 'utc', and timezone config is None, ask the user if they want to use the browser's tz via some popup (or some link/alert/notification)

const tz = Intl.DateTimeFormat().resolvedOptions().timeZone; console.log(tz);

if they select 'no', set it to UTC?

[wrobelda]

Any chances of seeing this in master sometime soon?

[VonZubinski]

@wrobelda and others who are looking for a solution, consider this temporary approach until the merge conflicts are resolved:

• Register a free account with https://cron-job.org
• Generate your API key in the settings menu of changedetection.io
• Set up the specific time schedules with cron-job.org and Pause/Unpause API-calls (https://changedetection.io/docs/api_v1/index.html#api-Watch-Watch)

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