Improve the WIFI Scheduler to allow Off-Times
Use case:
* As a user, I want to ensure WIFI is switched off at night.
* This must NOT include an automatic switch-on the next day.
Current status:
* The WIFI scheduler supports pairs of the form (From-Time, To-Time) only.
* A "To-Time" is mandatory and cannot be omitted.
* Outside these Offtime intervals, the WIFI is - unwanted - switched on.
Suggested feature:
* Provide a way to switch Off WIFI at specific times without enforcing a Switch On- Time.
Suggested solution in the User Interface:
* Allow to omit the "To Time" - Entry in the Wireless Off Time scheduler.
The user should be allowed to have entries with a "From" - Time only.
