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

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

expand Matrix3 with set, identity, copy, multiplyScalar, deteminant, clone;  Matrix3/4.getInverse will now optionally throw an exception; start Matrix3/4 unit tests

implemented Box3.transform, tested.  Removed Box3/Box3.scale as it doesn't work in the general case.  move tests to tests/math from tests/core to replace move of tested source files.