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

* 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

Simplify the Choice Widget and make it a TextBox variant.

Drive-by fixes:
  * ui.Collection: prioritize newer widgets during active widget selection
  * game.FullAction: fix incorrect cost function.
                     Full actions cost all available actions. Also
                     fix the cost check

Panicf includes a stacktrace and causes a debugger to halt.

The NPE is caused by any piled permanent with which TilesInRange is
called.

* 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