Also implement pan and zoom for 2D cameras.
Update the rendering tests to do these camera rotations. This matches
better the viewpoint used before the previous camera changes.
Affine transformations of homogeneous coordinates using 4x4 matrices are
quite common in visualization. Create a new math header file in the base
vtkm namespace that has common functions for such coordinates.
Much of this implementation was taken from the rendering matrix helpers.
With only a few exceptions for simple structures, we do not expose the
members of classes. Instead, we provide accessor methods. Do this for
Camera as well as add some helper methods.
The width and height are maintained out of necessity by the canvas. A
second copy was maintained by the camera, which was only used for
computing the aspect ratio and similar metrics for projections.
Having to maintain the width/height in two places is a bit of a hassle
and provides the opportunity for bugs if they get out of sync. Instead,
have the width/height managed in one place (the canvas) and pass them as
parameters as necessary.
