A series of perfomance enhancing changes. These are some of the code hotspots determined by JProfiler. These changes should be internal only and not affect library's public API.

1. Improved the use of generics in ComponentManager and ComponentMapper to reduce the need for dynamic casting at runtime.
2. Sped up Entity.isActive() method by allowing it direct access to the EnityManager's fields. This method is called very frequently.
3. Changed SafeArray to access the items array directly instead of using super.get(). Another frequently used method.

More profiling to come in the future.