for this to work properly you need the GL_EditorFramework project from https://github.com/jupahe64/GL_EditorFramework
just download it and add the GL_EditorFramework.csproj as an existing project to the Goombratlas solution
chances are that the Framework changed drastically since the last commit of this project so happy bugfixing!
No further support for this project is guaranteed, which means Pull Requests are pretty much useless