Added navmesh and updated tree texture

- Added HDR
- Redid the street lights. They're now slightly oranger. Some other lights have been edited as well
- Fixed some texture mistakes
- Made the elevator doors into a func_button, so you don't have to walk into them to teleport back to ground level
- Added some small light models throughout the map, mostly on the roofs and some indoor areas
- Added street barriers to indicate map boundaries
- Changed one of the easter eggs

Included a ceiling texture and a detail texture that I accidentally left out in the last update

Increased skybox resolution, and packed custom + L4D and CSS materials into the map