Allow excluding specific timeframes from updates

[Utzel-Butzel]

Right now updates run on fixed intervals. It would be useful to exclude certain times (e.g. nights) where no updates should happen.

Approaches

Simple: Add “do not update between X–Y” ranges.

Advanced

Use rrule to generate exact update times (very granular).

@smarthomeagentur Does the current PCB clock support rrule-based scheduling or a list of UNIX timestamps to wake up, or should we stick to exclusion ranges?

Benefits

Saves battery, avoids unnecessary updates, gives users flexible scheduling.

[smarthomeagentur]

I think this is a server side task. The epaper can always take a time in seconds when it should wakeup next. Optionally could.be wakeup via motion later...