Added ability to toggle between normal and slow mode, added flagEntityForRemoval() functionality to ECSEngine
Game features:
- Toggle slow mode.
Library feature:
- ECSEngine now has method to flag an entity for removal.
- The ECSEngine will then remove all flagged entities (and related comonents/systems) at the end of its update() method.
- This will be useful for self deletion, for example when handling collision, or taking damage.