Allow changing video device without recompiling

The video device can be set using the C22_VIDEODEV environment variable.
The default value is "/dev/video0". If the specified video device does
not
exist, or is inaccessible, the behaviour is undefined.
Remove redundant calculations from PseudoWorld
Warn, when Coilgun not loaded
Improve Kbui behaviour

- use a queue to store incoming commands
- properly die when Kbui::close is called