added Selection PostFx Shader by Konrad Kiss and Smally

To turn this feature on, enter SelectionPostFx.enable() at the console,
and make sure you use setSelection on a ShapeBase in view.

If you want to change the color, here's where you'll need to make
modifications in selectionShaderP.hlsl:

float4 e = float4(vis, 0, 0, vis); // <-- silhouette color
float4 ovr = float4(avgval, 0, 0, avgval); // <-- overlay color

ovr *= 0.4; // <-- overlay "thickness" (0.4 = 40% transparency for the
overlay)