New tunnels geometry added and item spawn optimization

Added in client download link

* Extended sky geometry to stretch on properly instead of ending abruptly.
* Changed sky and lighting to a darker evening using a custom sky texture.
Credits: evening_sky2 (link)[gamebanana.com] by Mr.Who

* Replaced dev textures with more palatable textures and made the claustrophobic room more open.
* Removed holes from the walls and added two crevices to each side of the grate so commons have more ability to swarm the grate.
* Moved throwable boxes down to the floor.

* Fixed nav on diagonal grates being unmarked and causing the horde sound to play and potential infected spawns on servers with certain plugins.