This commit enables three.js to manage the stencil buffer via material
properties.

This pull-request adds `renderOrder` functionality which  `Mesh` instances already have.

Actually use the loading manager in the CubeTextureLoader by passing it
to the internal ImageLoader.

LatheGeometry modified to use Vector2 and allowing axe choice by the
called.
The axe is designed by a letter because I didn't know where I should put
a constance definition.
The loop that create the geometry is not optimized for speed => the axis
test is in the inner loop.
Should not break any existing code.
Doc and exemple not updated yet.

this directly calculates the min and max of the bounding box instead of using the Box3 methods

LatheGeometry is a standard geometry but it's not processed by
parseGeometries of ObjectLoader.