The remove boost::shared_ptr and the rendering library branches where
developed simultaneously, and thus some of the rendering library
implementation was using boost::shared_ptr like the old code. Bring up
to date with the rest of VTK-m by using std::shared_ptr instead.
It is now optional to give a Camera object when constructing a View. If
a Camera is not specified, one is automatically set up by calling
ResetToBounds on the spatial bounds of the scene.
This makes it even easier to set up a view.
Generally we try not to expose the implementation details of how things
are stored in objects.
Also changed some arguments that should have been declared const to
actually be const.
The rendering classes do not actually manage windows, and window was not
descriptive of what this class was doing. We decided that the class was
mostly analogous to what we call a "view" in ParaView.