* In a couple of places I had to resort to if(IsHighContrast) but mostly
this is just using system brushes consistently or not assuming black
text.
* The default DockPanel theme doesn't work well, so make a minimal high-
contrast theme for it and assign it everywhere.
* The pipeline flow was using fixed colours, use system brushes for the
different elements and switch based on high-contrast to ensure active
and inactive stages are visible (using ActiveCaption looks bad on
normal themes because it's a big block of colour).
* For some reason the flat toolstrip renderer doesn't handle white-on-
black themes, but the system one does. It's a little clunkier but it
shows up correctly without writing tons of custom painting code.
* Range histogram uses a properly contrasting colour for the border.
* Treelist views use a better system colour for selected rows when
inactive and hovered rows (when high contrast).
* Mesh view grids have a system background instead of white
* Various things (pipeline state, mesh viewe) set text colour when
colourising backgrounds of things instead of assuming black.
* You can't set SplitterDistance unless both MinSize values will be
respected, which needs a big enough window. Smaller than that, we just
have to skip setting the size.
baldurk