- switched skybox texture to a gmod one
- automatic doors can be opened by physics props
- added nav_mesh
- minor visual and clipping changes

- fixed a spot where you could look through the map
- updated performance issues (area portal + fade distances added)
- removed the real-time mirror (caused visibility issues)
- added some clips and other movement improvements:
- added box to a vent, so no crouch-jumping is needed
- added auto-crouching to the vents