Duh! why count children, when you know we have a mask of children, if the mask is 0 we are a leaf!

=====
**Before**
```
Running Time	Self		Symbol Name
153759.0ms    6.3%	23132.0	 	OctreeElement::isLeaf() const
126403.0ms    5.2%	92242.0	 	 OctreeElement::getChildCount() const
 34161.0ms    1.4%	34161.0	 	  numberOfOnes(unsigned char)
```
**After**
```
Running Time	Self		Symbol Name
3022.0ms    4.0%	3022.0	 	OctreeElement::isLeaf() const
```