Fix a lot of high-contrast inconsistencies or brokenness. Refs #315

* 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.

renderdocui/Windows/TextureViewer.cs

@@ -372,6 +372,17 @@ namespace renderdocui.Windows
 
             InitializeComponent();
 
+            if (SystemInformation.HighContrast)
+            {
+                dockPanel.Skin = Helpers.MakeHighContrastDockPanelSkin();
+                zoomStrip.Renderer = new ToolStripSystemRenderer();
+                overlayStrip.Renderer = new ToolStripSystemRenderer();
+                subStrip.Renderer = new ToolStripSystemRenderer();
+                rangeStrip.Renderer = new ToolStripSystemRenderer();
+                channelStrip.Renderer = new ToolStripSystemRenderer();
+                actionsStrip.Renderer = new ToolStripSystemRenderer();
+            }
+
             m_Goto = new Dialogs.TextureGoto(GotoLocation);
 
             textureList.Font =