Adding a Dark mode for the JSF client

[StefanSchubert]

Is your feature request related to a problem? Please describe.
For those of us who are sitting in the late hours before the PC, an optional dark mode would be nice.

Describe the solution you'd like
Minimal Solution: The user profile contains a setting, to activate the dark mode and the UI acts accordingly.
Max-Solution: same as min, but I could configure a time range in my user profile, when to automatically switch to the dark mode and cycle back to the normal one.

Describe alternatives you've considered
None

Additional context
None

[StefanSchubert]

I parked it in Milestone3 but it could be tackled any time or moved along later milestones as it's more a convenience request.