Most of the time, you just match the WorldAnnotator with the canvas of
the same type. Rather than make the user specify it every time, add a
method to the canvas that creates a "good" WorldAnnotator to use with
it. Then, if a WorldAnnotator is not given to the View constructor, one
is automatically created from the Canvas.
The template parameters on vtkm::rendering::View are unnecessary. All
three of the templated classes are polymorphic (with virtual functions).
Thus, you just have to specify them at the constructor. Removing the
template parameters makes the syntax a bit cleaner and removes some
unnecessary duplication in the executable.
Removing the template does mean we cannot optimize in the future.
However, I expect us to start using more virtual methods rather than
less, so I think this is a move in the right direction.
