Apply our selected text color to haeaders (h1 and h2)

Apply our selected text color to haeaders (h1 and h2)

This was previously happening in the empires client, but now we move
this up to the top-level.

Note that we don't use the selected text color at minimal font sizes
(such as in the "body" element in general). This is because we want a
high contrast there for maximal legibility. So we introduce an
additional named --text-fo-color-max-contrast which is set to pure
black.