Added convenience method worldToLocal(Quaternion) to spatial.

[zzuegg]

This PR adds the convenience method worldToLocal for Quaternions, i added a test that shows the usage when transferring a spatial to a different Node.

[codex128]

I suggest using isSimilar for equality checks so it doesn't fail on round-off error.

[zzuegg]

Good point

[zzuegg]

I am going reimplement to get rid of the unneccesary allocation.

[codex128]

I don't know how quaternions work, so take this with a grain of salt.

[codex128]

This doesn't look right to me if you're trying to normalize and invert the rotation. From looking at Quaternion, it seems like norm should be changed like this:

norm = FastMath.invSqrt(norm) / norm;

[zzuegg]

Generally i agree, using jme math i have not yet managed to create a non normalized quaternion.

        for (int i = 0; i < 1000000; i++) {
            Quaternion quaternion=new Quaternion().fromAngles(FastMath.nextRandomFloat()*-360,FastMath.nextRandomFloat()*360,FastMath.nextRandomFloat()*360);
            Quaternion inverse = quaternion.inverse();
            float norm = quaternion.norm();
            //norm = FastMath.invSqrt(norm)/norm;
            System.out.println(norm);
            quaternion.set(quaternion.getX()*-norm, quaternion.getY()*-norm, quaternion.getZ()*-norm, quaternion.getW()*norm);
            if(!quaternion.isSimilar(inverse,0.000001f)){
                System.out.println("Fail");
                System.out.println(quaternion);
                System.out.println(inverse);
                System.exit(1);
            }
        }