DisplayObjContainer addChild / removeChild performance fix

methods reverted back to original implementation to avoid performance
issues, expecially in addChild because of the redirection on addChildAt
that is very poor
in performance
small improvement in multiplyColor management
Change in quad / image creation to extend basequad inheritance

Now every object of a predefined size can inherit from BaseQuad.
Previously was possible only for object build with 0,0 as center.