ModuleWidget integration with CpuGraphicsScene

Replace ModuleGraphicsItem in CpuGraphicsScene with ModuleWidget. This is also an opportunity for refactoring CpuGraphicsScene.

added Feature Refactor labels

As ModuleWidget has all responsibility of ports, remember to delegate port control to module widgets or perhaps use signals and slots between ports and the graphics scene.

This particularly concerns disabling the port actions in the context menu when the scene layout is locked.

mentioned in merge request !45 (merged)

assigned to @johku144

mentioned in merge request !46 (merged)

closed with commit ea919ce0