Reorganize tests
Make test files smaller (sperate tests for Vector2, Vector3, lists, Matrices and so on...)
Put tests into folders matching their library
It allows also a better overview where we need to improve our test coverage in the future
Add tests for vector_math_64. The tests are generated from the 32bit tests. Fix some tests that fail due to precision changes.
Add a way to run the unittests in a browser. Running in dartium is not that important, but it is important to check if the results of the dart2js generate code behaves the same as in the VM.