DiscardCardAction should be able to remove cards from any zone

[StefanoFiumara]

Currently, DiscardCardAction is hardcoded to remove cards specifically from the hand into the discard pile.

In the future, we may want to use DiscardCardAction to discard cards from different zones.

• Update the action listener in HandSystem to move cards from any zone into the discard pile.
• We may possibly want to move the listener into a different system (PlayerSystem?)
• Add an easy way to move cards between zones on the player object (PlayerSystem?)