Small Ray collision optimization & Fixed test cases

Few small changes:

Ray.js pointInTriangle:
 * Lazy evaluation of u and v to avoid unnecessary multiplications
 * Replaced division by a common factor only to compare with 1 with comparison with the factor itself

Ray.js test:
 * Changed box creation code to use the Box class to avoid the triangle handedness warnings
 * Added some corner case tests to be sure that optimization works.