Vectmath - bring vector_math to three.dart

Here comes the pull request for switching to use the <b>vector_math</b> library for three.dart.
I believe this will benefit three.dart greatly since the Dart vector_math library will be the most performant solution going forward with <b>SIMD</b> support etc.

The changes are many (but small ;-) and I will continue to issue pull requests for adding missing functionality to vector_math, thus reducing the number of vector_util and matrix_util functions.