Allow VistaVertexArrayObjects to store std::shared_ptr to Vertex-/IndexBufferObject.
Allow VistaVertexArrayObjects to manage the livetime of the Vertex-/IndexBufferObject they use thorough the use of std::shared_ptr. This can be useful to avoid the deletion of Vertex-/IndexBufferObject which are still used by a VistaVertexArrayObjects.
std::shared_ptr can now be used as aguments for: SpecifyAttributeArrayFloat(), SpecifyAttributeArrayInteger(), SpecifyAttributeArrayDouble() and SpecifyIndexBufferObject()