Implement new generic input concept

Should provide keyboard and mouse per se and a concept for integrating other input devices (game controllers, space mouse, ...)

The issue names no files, tests, or entry points. Start by locating the existing keyboard and mouse input handling, then determine the integration points and scope for supporting other devices; done means a generic input concept supports keyboard and mouse and can accommodate devices such as game controllers and space mice.

Written by the indexing model from the issue text.