Fixed nodegraph getting rebuilt/overwritten by the game.

Minor additions and changes.

Full changelog:
- Added buttons for opening/closing the garage doors at the gas station.
- Changed various static prop_physics, prop_dynamic and prop_dynamic_override entities to prop_static.
- Minor cosmetic additions to some buildings.

Minor fixes.

Full changelog:
- Added two decal textures that were missing for players without HL2: Episode Two.
- Fixed the issue where a fence model from HL2: Episode One would override a fence model from HL2 (with the same name but a different shape) in other maps. Also prevented possible conflicts for other models that have different versions between HL2 and Ep1/Ep2.

Update that adds nodegraph and navmesh for NPCs, soundscapes and pieces of missing content. Also various minor changes and fixes.

Full changelog:
- Added basic nodegraph and navmesh for ground NPCs.
- Added usable train track switches.
- Added soundscapes and some other ambient noises.
- Improved water material with fading near the shoreline (thanks to Rush_Freak for the tip).
- Increased fade distance for fluorescent light props.
- Increased lightmap resolution on various surfaces.
- Included some textures and models that were still missing.
- Lowered some trees near airstrip runway.
- Moved map thumbnail image, per Rubat's suggestion.
- Fixed cubemap errors on map load.
- Fixed gate causing the screen to go black when dragged with the physgun.
- Fixed gate barely moving when shot with the gravity gun.
- Fixed light origin errors on various props.
- Fixed two overlays that were not applied properly.
- Fixed missing geometry underneath pier shops.
- Fixed tree prop near carousel slightly floating.

Added map icon.

Initial Workshop release.