Implement Free Look and Zoom in Cabin View

[DasCapschen]

See Issue #87 , this implements a free moving camera in the cabin view and zooming.

Changes:

• CameraState is an Enum now
• use clamp() instead of if > elif <
• always set mouse mode to captured
• camera rotation in cabin view
• camera zoom (field of view) in cabin view

Known Issues:

• Mouse is visible in Grey Train, but not in Red Train

[Jean28518]

Thank you very much! I will review the changes in the next days.

I will concentrate on #87 after I finished #86

[Jean28518]

Thanks :)