dark themes

[Caolán McNamara]

Looking at https://bugs.documentfoundation.org/show_bug.cgi?id=102778 w
hich is "insufficient contrast with dark themes" for the page layout
icons in the writer status bar I see that we have...

a) a breeze dark theme
b) a VCL_ICONS_FOR_DARK_THEME variable which re-colorizes icons to fit
a dark theme better (?)

any thoughts on when detecting that gtk3 has a dark theme enabled if we
should auto-default to the breeze dark theme or go down the
VCL_ICONS_FOR_DARK_THEME route ? Or something else.

C.