Physics: complete the definition for ShapeGroup.
SceneGraph: added Object::setParentKeepTransformation().
Physics shape rework #7: renamed Physics namespace to Shapes.
Shape rework #8: updated documentation.
Math: fixed matrix tests (spotted by Clang).

Either GCC 4.8 poorly implements C++11 or it already has support for
some proposed C++14 feature, which allows to elide successive
initializer braces.