app: set default simulation intent to relative colorimetric.

We should set these explicitly, otherwise it will usually default to the
first of the enum, which is perceptual (which is usually not a proper
choice).

Relative colorimetric is usually the recommended default.

app/core/gimpimage.c

@@ -783,6 +783,10 @@ gimp_image_init (GimpImage *image)
 
   private->metadata            = NULL;
 
+  private->simulation_profile  = NULL;
+  private->simulation_intent   = GIMP_COLOR_RENDERING_INTENT_RELATIVE_COLORIMETRIC;
+  private->simulation_bpc      = FALSE;
+
   private->dirty               = 1;
   private->dirty_time          = 0;
   private->undo_freeze_count   = 0;