Version 2.4.1.1 breaks the build

Upgrading from nuget package `SharpGL.WPF` 2.4.0 to 2.4.1.1 introduces several compiler errors, eventually due to a missing or inaccessible dll.

```
The type or namespace name 'SceneGraph' does not exist in the namespace 'SharpGL' (are you missing an assembly reference?)
The type or namespace name 'ShaderProgram' could not be found (are you missing a using directive or an assembly reference?)
The type or namespace name 'SceneGraph' does not exist in the namespace 'SharpGL' (are you missing an assembly reference?)
The type or namespace name 'GLColor' could not be found (are you missing a using directive or an assembly reference?)
The type or namespace name 'OpenGLEventArgs' could not be found (are you missing a using directive or an assembly reference?)
The type 'OpenGLEventHandler' is defined in an assembly that is not referenced. You must add a reference to assembly 'SharpGL.SceneGraph, Version=2.4.1.1, Culture=neutral, PublicKeyToken=27fc851303210b27'.
```

#159 seems to be related.

I don't use scenegraph as 95% of my scenario is based on low level OpenGL API. The remaining 5% are simple line/quads drawings.

Reproduce the upgrade from SharpGL.WPF 2.4.0 to 2.4.1.1 in a WPF project and compare the package contents and assembly references, especially SharpGL.SceneGraph. Read issue #159 for related context. Done means the affected namespaces and types resolve and the project builds after upgrading.

Written by the indexing model from the issue text.