Vec4.toString() should not be final

[jonbarril]

I dare say that toString() in any class should not be final as extensions based on such classes can never implement their own toString() with whatever formatting the subclass may need.

In the specific case of Vec4, to utilize WorldWind as a platform, Vec4 parameters are required. However, it is nice to be able to extend Vec4, which lacks certain tech/math niceties, and to do a better job of compact formatted printing. There are work arounds but not making toString() final is by far the simplest solution and was probably done originally in 2013 out of habit.

--jon