fix three missed conversions to closures.  switch to extending math prototypes rather than replacing them.  This is to ensure that types created in closures within a type's prototype definition get their prototype updated with the full definition.

Renamed Vector3 projectPoint() to applyProjection() as per @WestLangley suggestion in bb873d16.

Changed back some .projectPoint() to .applyMatrix4() as per bb873d16.

@WestLangley I've changed most of the vector.applyMatrix4() to vector.projectPoint().
Feel free to change back the ones that aren't needed (or let me know which ones can need to be changed back and I will do it).

Plane: Removed normalize() from setFromNormalAndCoplanarPoint and added it back to setFromCoplanarPoints. As suggested in 5c6b5746.

CanvasRenderer+SVGRenderer: Removed 2D clipping for Face3/Face4 elements as the projector is already taking care of that.

update math constructors to not copy when provided explicit initial values per @mrdoob: https://github.com/mrdoob/three.js/pull/2902#issuecomment-11999928

Frustum bug fix: clone and constructor should be real copies.  Fix bug in unit test to catch this in the future.

Removed Vector* add() to addVectors() and addSelf() to add(). Same with sub, cross, min, max, lerp... Renamed Matrix* and Quaternion multiply() to multiplyMatrices(), multiplyQuaternions() and multiplySelf() to multiply(). See #2860.
Good thing we have a ton of examples to make sure nothing is broken. The unit tests also helped. However, I suspect I've left something unchanged.

Added .add(), .addColors(), .addScalar(), .multiply() and .multiplyScalar() to Color. Removed ArrowHelper from DirectionalLight too.

Also, code clean up here and there.

Add missing space
Fix isIntersectionSphere
Addunit test for isIntersectionSphere

Tets if two spheres intersect

Frustum.contains -> intersectsObject, containsSphere->intersectsSphere, removed Frustum.containsAnyPoints, .transform.  Update unit tests accordingly.

Renamed .multiplyMatrix* to .applyMatrix* and .multiplyQuaternion to .applyQuaternion as suggested by @WestLangley in #2860.

Makes the code so much nicer imho...

always use local var planes = this.planes in Frustum. fix common include to require Sphere before Frustum.