- Made component fetching a bit more direct.
- Now ComponentMapper is the actual collection of components so there is
less pointer chasing when doing a mapper.get(entity) call. It also
provides 'data()' method to access the backing array directly.
- Fixed a silly mistake in which the comparison made for growing the
poolsByType array in ComponentManager was reversed, so it worked but it
always copied the array. Now it does the proper comparison and grows
only when needed.