Sync brightness level across multiple monitors

[OliverPerssonB]

Is your feature request related to a problem? Please describe.

This is a minor but welcomed addition to the program. It would be nice to have a checkbox for syncing settings across all displays, as it is common to want to have the same settings on both monitors.

Describe the solution you'd like

Add a checkbox to the gui which syncs settings across the monitors.

Describe alternatives you've considered

Additional context