Feature/cleanup aabb

I tried to split up my PR by feature, but that is hard (to much work). My current plan is to send many small PRs that go chronological through my big PR. I try to do group together commits that make sense. But this means that I may have things that aren't 'perfect' after this PR, but a later PR will fix this.

Remove call chaining from the AABB classes. I also fixed the indention for constructors, but I screw it up for the containsAabb methods. I tried to fix it, but it will make later pull requests more difficult due to merge conflicts as I already fixed it in a later commit that is not included here.

Aabb2.fromBuffer is missing in this PR, but I have a later one that will add it to have a equal interface for 2 and 3 dimensional AABBs. I have to add Vector2.fromBuffer first.

Always using the private variables is related to a later PR and improvments for dart2js. A later PR will rename the private variables, so that they are unique for every class in this library.