Added ProduceCommand, which, when executed, produces a constructor given
value into the supplied scope. It will, at first, be used to support
scope usage in Add/ForwardedAdd/Restore/Destroy/Remove commands. Add
command requires a model factory, which may be given through a
ProduceCommand.

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>