Feature: CLI option for icon contrast

[alex-nitrokey]

Nitrokey App is supposed to decide whether a black Nitrokey icon or the inverted version is used (e.g. if the tray bar is already black). Sometimes this may not work or the user has reason to choose the light version. Therefore, it would nice to have a cli option to toggle this feature manually.

This could read something like --light-icon or --icon=light if there should be a option list possible.