OrbitControls: Added support for constraining azimuthal rotation

Avoids unnecessary renders and object saves.

Support BufferGeometry in Box3.setFromObject()

Update Scene.html

it's -> its

Update ArrowHelper.html

Fixed 'WebGLRenderer.clear' method's description

WebGLRenderer's documentation incorrectly stated that if no parameters were passed to it, the 'clear' method will not clear any buffers. The default behaviour is in fact the opposite: if an argument is undefined, the corresponding buffer will be cleared. The document now correctly describes the default behaviour.
Source code of the method: https://github.com/mrdoob/three.js/blob/master/src/renderers/WebGLRenderer.js#L368

PnlTri.js Rev. 2.0: now handles vertices and edges on other edges (co-linearity)

fix ColladaLoader- result.scene must be a Scene to be renderable