Rather than force all dispatchers to be templated on a device adapter,
instead use a TryExecute internally within the invoke to select a device
adapter.
Because this removes the need to declare a device when invoking a
worklet, this commit also removes the need to declare a device in
several other areas of the code.
Changed the "default" ColorTable preset from "cool to warm" to
"viridis." Also made a default constructor for ColorTable that sets it
to this default preset.
The main reason to change to viridis for the default is that it is in
LAB space. We are concerned that having the default ColorTable preset
being Diverging space could lead to users using that color space
inappropriately.
The problem is that there is no good "default" constructor for
ColorTable. The previous default constructor created an empty color
table, but that would be confusing if someone actually tried to use it.
We could set ot to the default preset, but the default preset uses the
diverging color map, which could foul people up if they actually want to
edit or create their own color map. Instead, force the declaration of
ColorTable to indicate what you plan to do with it.
The new and improved vtkm::cont::ColorTable provides a more feature complete
color table implementation that is modeled after
vtkDiscretizableColorTransferFunction. This class therefore supports different
color spaces ( rgb, lab, hsv, diverging ) and supports execution across all
device adapters.
