[feature:] Population specific fleet interactions

[msupernaw]

Describe the situation that led to the request and a solution

Currently, fleets and populations are defined globally with all fleets operating on all populations. FIMS would be greatly enhanced if the user was given the ability to have explicit fleet/population interactions, especially when we develop spatial components.

Alternative solutions

Giving the user the ability to assign fleets to a population:

population_1$AddFleet(fleet_1$get_id())
population_1$AddFleet(fleet_2$get_id())

population_2$AddFleet(fleet_3$get_id())

Statistical validity

No response

Additional context

No response