Changed the iron facade to the general one, fixes #332

If the facades feature is disabled it will cause a NPE because it is trying to create the specific iron block facade, which is not possible under this conditions.

For whatever reasons it chooses the glass facade. Which I personally find more convenient, because it shows the anchor clearly instead of hiding it like a opaque version is doing.
This might chance depending on the installed mods, but I would consider a possible changing icon the better solution to crashing.

The achievment tab itself is already sophisticated enough to hide disabled features.
So I do not see any reasons currently to split it up and disable them explicitly if the specific feature is disabled.

Fixes #332