WireframeHelper: Added edgesOnly option and line color option. Also some...

... cleanup.

The `edgesOnly` option works with `THREE.Geometry` only. (The face-edges relationships are not readily discerned with `THREE.BufferGeometry` -- save for later.)

Demo: http://dl.dropboxusercontent.com/u/63997063/Three.JS.WireframeHelper.html

![screen shot 2013-12-22 at 8 11 49 pm](https://f.cloud.github.com/assets/1000017/1798855/4d61bc4c-6b75-11e3-84cc-5ad28e5df1d5.png)