Implement generic object pool

[n8rzz]

Instead of creating and destroying aircraft instances pool them for re-use.

• This will require an additional layer between the AircraftController and the AircraftInstanceModel and will also require new methods.
• Before any of this work can happen, it would be best if the loading of aircraft were decoupled from the AircraftController.

https://sourcemaking.com/design_patterns/object_pool

[n8rzz]

If this is made to be generic, there will probably also need to be a factory layer.

ObjectFactory -> ObjectPool -> ReusableModel

[n8rzz]

This will depend on #53 in order to add Waypoint and PositionModel

[n8rzz]

adds #120 and #121 for future additions to the pool