Simple ProjectImporter for GoProjects

Created a Simple Project Importer, which creates a module for the new project
and marks the "src" folder as SourceRoot, if it exists(even though we don't make use of this feature).

During the Process, the user can choose the Go-SDK, which will be used.

In order to use the Importer, the User has to choose the "Go"-External Model. "Import from existing source" would require us to have a single project-file, which stores all the information about the project (similar to .project of eclipse), so it is not suitable for go projects.

#503 #230