Implement `attribute_5` (splash)

[j-wielg]

Write logic for the splash attribute. After attacking a unit, this attribute should inspect every tile in a 1-tile radius of the enemy which got attacked, and attack every enemy within that radius using half as much attack power as usual. DO NOT call the .attack or .being_attacked methods in the attribute logic (cards affected by splash damage should not be allowed to counter-attack). The damage calculations should resemble those found in Classes/troop.gd

See here for more info on attributes.

Requirements:

• Code should be located at Attributes/Troops/Logic/attribute_5.gd
• Code should contain a comment labeling it as the splash attribute
• Code should not call Troop.attack or Troop.being_attacked methods

[mayleenliu]

This is currently being worked on