This is useful under Android where the palette is apparently not set to
something matching the darkmode setting but the Qt Quick Material style
nevertheless seems to follow the darkmode setting. So we just want to take
the darkmode setting into account for assigning the appropriate icon theme
and ignore the palette.
This is now `QOperatingSystemVersionBase::OSType` causing a warning about
an implicit conversion. Making an explicit cast to whatever type
`os.type()` actually returns (depends on the Qt version) this warning does
not occur anymore and the code should still compile with any Qt version.
Whether an application can retranslate the UI dynamically likely differs
from whether the other appearance related settings can be applied
dynamically so this needs to be configurable individually.
Additionally, the environment settings can never be applied dynamically so
the notice on that page should always be shown.
For some reason the tool button's palette changes back to the old palette
when applying changes. So it cannot be used to hold the intermediately
selected paletted.
* Set the default icon theme when applying Qt settings and the "system"
theme is supposed to be used but none could be determined by Qt
* Use a bundled icon theme depending on whether the current palette is
light or dark
* Apply the default not only under Windows anymore; supposedly this makes
sense under any platform where Qt cannot determine the icon theme for us
At least the documentation of `QIcon::setThemeName()` sounds like it could
make a difference:
```
The name should correspond to a directory name in the themeSearchPath() …
```
This makes the annoying hasBeenShown() check in each apply()
and reset() implementation unnecessary. It should not break
anything because if the page hasn't been shown there is nothing
to reset/apply anyways.
Martchus