change cacao.Command to CommandData and related

[lucamrgs]

Is your feature request related to a problem? Please describe.
In the CACAO spec, what we now call Command object, is actually the command-data type.

Also frankly I think that using Context.Command.Command, or any cacao.Command.Command, is quite counter-intuitive.

Describe the solution you'd like
context.CommandData.Command
cacao.CommandData.Command