Add gamma correction to screen space renderable (SSR) shader, property for SSR and default value gamma = 2.2 for sky browser display copies

modules/base/shaders/screenspace_fs.glsl

@@ -32,6 +32,7 @@ uniform sampler2D tex;
 uniform vec3 color = vec3(1.0);
 uniform float opacity = 1.0;
 uniform vec4 backgroundColor = vec4(0.0);
+uniform float gamma = 1.0;
 
 Fragment getFragment() {
   Fragment frag;
@@ -44,5 +45,6 @@ Fragment getFragment() {
   }
 
   frag.depth = vs_depth;
+  frag.color.rgb = pow(frag.color.rgb, vec3(1.0/(gamma + 0.000001)));
   return frag;
 }