Please add some changes on 3.x to the 2.x branch

[aismann]

@halx99
Please add this changes to the 2.x branch (its so much better have it now, as let it only comes later):
[ ] Implement drawArraysInstanced and make instanced draw more common use
[ ] Improve DrawNode, don't create backend::Buffer always

Please also this: Add ax::Color (not change) so no API change is there
[ ] (Change)/Add underlaying color type to Color4F aka ax::Color

---

Still on the 3.x branch:
Remove all deprecated stubs

All Box2D 3.x stuff:
Make Box2dTest of cpp-tests works on box2d v3
Make Box2dTestBed of cpp-tests works on box2d v3
Remove chipmunk
Remove core/physics based on chipmunk
Remove ChipmunkTest from cpp-tests
Remove ChipmuniTestbed from cpp-tests
Reimplement core/physics with box2d v3, not all API compatible with axmol-2.x