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.

This allows to not use the internal game state directly from client
code.

This fixes highlighting when an action needs no targets at all.

* 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

* implement dopping piles
* implement simple spell targeting
* add some simple spells

Panicf includes a stacktrace and causes a debugger to halt.

* fix a lot of target and action bugs
* check target selection before adding it to the prompt
* use the store view for stores on the map
* fix card highlighting in CardGrid
* Only prompt for Upkeep-/DiscardActions if appropriate
* Add helper for areaEffects granting new FullActions
* Add Target() helper selecting the first target to the Action interface
* Fix BuyAction and DiscardAction targets
* Remember the stores a player has seen