Stop rendering the tile under the room/trap ground tile.

Thanks to oln for that, it was obvious but my mind would have make it this time. XD

I also remove the gold on ground when all the gold has been dug.
It is misleading and shouldn't be done until we have a better tile for that.
Removed the useless and empty 'Spells' tab from in-game menu.

Let's readd this one when actual work on spells has started.
Added the new spider model thanks to Danimal

Fixes #269
Fixed trap ground tile visibility in certain cases.

I also made the animation state fall back to "Walk" when "Flee" is requested
and the "Flee" animation doesn't exist.
This is preventing certain creatures from looking weird when fleeing,
such as the Lizardman.
Fixed materials parameters for values format and bounds.

This fixed #41 for me and can't hurt anyway.

Most materials touched were indeed linked to the Golem worker, but not only.
Hard-coded mis-set tiles types in the code.

Fixes #240

Of course, the actual solution is #14
Hopefully fixed the Cavehornet translucent wings.

Fixes #267
Quick-fixed the spike trap ground tile disappearing when building it.
Used the display ground tile api for rooms as well.
Merge pull request #258 from Bertram25/development

Stop rendering the tile under the room/trap ground tile.