Left 4 Dead Survival Maps - No Mercy: Version 0.5

The Street:
- Added new Survival Map

Gas Station:
- Fixed some overlays being cut off
- Fixed an area not being blocked
- Fixed some props not showing in game

The Hospital:
- Fixed some overlays being cut off

Misc:
- Improved NAV across all maps
- Built cubemaps for all maps
- Added stringtables for all maps