Removed unnecessary fields from `Person`. Updated constructor.
## Person animation refinements. Reset `SpriteAnimation` feature.

Cleaned up and refactored animations is `Person`. `SpriteAnimation`s are
now reused within `Person`. `SpriteAnimation` can now be reset, to
properly reuse it. Idle stance is now custom hardcoded animation, to
unify animation handling in `draw` method.

Cleaned up main app accordingly.
Added `toString` to BoardPosition.