equals(quaternion) {
        return this.elements[0] === quaternion.elements[0]
            && this.elements[1] === quaternion.elements[1]
            && this.elements[2] === quaternion.elements[2]
            && this.elements[3] === quaternion.elements[3]
            && this.axisOrder === quaternion.axisOrder;
    }
Checks if 2 quaternions are equal

     returns:
     @isEqual (bool): whether the quaternions are equals or not
*