SpecialNamed assets
A special named asset is one that isn't on disk, but is referenced by a specific name.
For example, you might make a texture that is called "black", then you can load that
texture using normal Library.Get functions, which means you can reference "black" in
materials etc.
Added "MeshEntity" in Engine addon (replaces StaticMeshEntity)
BspMap importer sets brush models as SpecialNamed models
Updated ents to use MeshEntity instead of StaticMeshEntity