Cleanup on Vector3 and GCVector

I started out doing a quick bug fix on Vector3 and wound up doing a bunch of stuff, so I figured I'd submit it as a pull request. Full change log is here:

* Fix for Vector3 Members not being accessible in playground (not marked as public)
* Added element-wise vector and scalar math to Vector3
* Replaced Vector3.equalToScalar() with an overloaded equality operator
* Added lerp to Vector3
* Added a couple convenience init and dot/cross product methods to Vector3
* Created unit tests for Vector3
* Added some convenience init functions to CGVector
* Added scalar addition/subtraction to CGVector
* Made lerp in CGVector more readable by simplifying it from element-wise lerp
* Updated the unit tests in Vector3

Let me know if you have any changes you want me to make before merging!