Cache graphics bounds instead of iterating over all contained paths over and over again

For embedded shapes, this already was the case, but for AS3-drawn ones, we only cached bounds on the path level
Merge pull request #969 from tschneidereit/master

Cache graphics bounds instead of iterating over all contained paths over and over again
Abstract removal of old and addition of new children in a timeline into one function

Just a shallow façade for now
Shorten some var names
Add DisplayObject#_setTransformMatrix and use it everywhere

This gets rid of lots of object allocations, and gets rid of three separate, slightly different, copies of the same transform update code
Merge pull request #973 from tschneidereit/master

Display list updating optimizations
Use internal Loader properties.