Implement `attribute_4` (Scout)

[j-wielg]

Implement the scout attribute, which removes fog-of-war in a two-tile radius. See the Troop.clear_fog method in Classes/troop.gd to see how the attributes contribute to fog clearing.

See here for more info on attributes.

Requirements:

• Code should be in Attributes/Troops/Logic/attribute_4.gd
• Code should inherit from the TroopAttribute class, and contain a comment labeling it as the "Scout" attribute
• Code should override the clear_fog function and return an array containing the tiles to clear