Nav mesh fix

Minor fix.

Along with various small fixes:
- Updated the shipping container colours, since the Nuke update changed the way these were rendered
- Updated footstep sounds on various parts of the map to correctly reflect the surface

Final pre-contest update.
- Map is fully detailed.
- Changed the entrances to A: the back alley now only goes to the side entrance, and the main entrance is now the only way to get to the long hallway/office.

Fully textured the warehouse, and various other changes.

Mainly an aesthetic update and texture overhaul. Most things are now textured (some are temporary), and many places are detailed.

Many changes, including large overhauls in some sections. The major things:
- A site's side corridor (going from T main to CT main) have been extended and changed to closer quarters, removing the long sightline and adding extra travel time.
- Added numerous boxes/obstacles to A site and its surrounding corridors, to promote more close quarters action.
- Added a second entrace to B site, with a smaller sightline.
- Removed B's upper and lower CT areas (the side entrance is still there), replacing it with a ladder room ("Red").
- The long sightline near CT spawn going from A's halls to B's halls has been removed.

- Added some shipping container props (especially on/near A, and near B)
- Changed the loading dock on B, added more cover
- Added detail/props to the interior of the warehouse in Mid
- Added a ditch in the field between A and Mid
- Various other small changes/additions

Added a catwalk to A site, and changed the halls from CT spawn to A.