Draft: Bookmark unused libraries.

Closes #67 (closed)

This MR removed the following libraries:

• src/GksGPU
• src/GksMeshAdapter
• src/GksVtkAdapter
• src/pythonbindings (moved to root folder)
• DemCoupling
• Traffic

It also removed the targets:

• TrafficTest
• GKS

The reason is, that those libraries are unmaintained. We store the commit hash here: #67 (closed).