Implement captain recall

[T00L00]

Desired feature:

• Player has to be within a certain range of a captain in order to recall.
• Player presses a button to recall a captain.
• Selected captains for recalls should have a visual indicator.

Questions to address:

• What button initiates recall?
• What if multiple captains are in range? Do they all get recalled? How do we fine-tune recalling so that the player only recalls who they want to recall? I'm thinking maybe we just implement an RTS click and drag to select captains they want to recall.