Some fixes

I wanted to split this into several requests, but GitHub added commits made after request here too, and I'm not that great git user, so here we go:

1) fix unpaired mouse over/mouse out events
This one is for situation when we send MouseOver event, then updateCollider fires and changes _previousCollidingObject, so we never actually get MouseOut event for that object, but we do get MouseOut for some other object which did not receive MouseOver yet.

2) fix ObjectContainer3D bounds calculation
Max* functions actually return Max for largest object in container, not container as a whole (which is probably not what was intended). This version accounts at least for child transition (works well for me)

3)added removeChildAt function
For me this function seems pretty useful for simple usage scenario such as "remove all children". Without such function it requires function chaining: removeChild(getChildAt(index)), which is additionally slower because of unneeded call to indexOf()

4) OBJParser: do not create zero-length geometries
Got that one on OBJ models that our artists created, so that was not intentionally malformed input

5) check for zero-length data in CompactSubGeometry
To help detect situations as with OBJParser, as it throws exception later anyway.

6) normalize normals and tangents after transform
Pretty much self-explaining - normals must be normalized