move shaders to .glsl files and stringify to .h file.

add crude screenshot facility (using F1 key), it can also be used for debugging
start with shadows using shadowmap, not working yet
add experimental 'ignore' body index in raycast, using b3HitInfo.m_m_hitResult2

btgui/OpenGLWindow/Shaders/createShadowMapInstancingPS.glsl

@@ -0,0 +1,10 @@
+#version 330
+precision highp float;
+
+
+layout(location = 0) out float fragmentdepth;
+
+void main(void)
+{
+	fragmentdepth = gl_FragCoord.z;
+}