Fix path selection choosing a to big step, since the next step
was determined by the moving range and not the actually available
movement tiles.

Fix generating a target for the AI by introducing a dummy action
to support "enemy" target constraints.

it is currently not implemented by the rules

Also make more state methods private.

* Implement move artifact action
* Fix widget update memory leak
  * update the highlights not during on each frame
  * do not update the unchanged label of a button
* Allow to exit the game by pressing 'q'
* Implement some cards from the magic set
* Improve permanent formatting
* Some tweaks to UnitAI code