Hard-coded widget state colours (error, warning, health etc.)
are replace by a central palette class, which also takes care
of determining if KeePassXC is in dark or light mode.
Colours expected to be used as background for normal text
were tested for WCAG level A compliance. Health colours were
adjusted for better harmony with the application theme and
tested for sufficient contrast with a colour blindness simulator.
Fixes#4407Fixes#4637
Additional changes:
- Fix reference entry colour being incompatible with dark themes
- Fix QWizard page being too bright in dark mode
- Prevent unfocused wheel scroll changes to theme setting
