This function adds the default decision types to a conservation planning
problem(). The default types are binary and are added using
the add_binary_decisions() function.
add_default_decisions(x)problem() (i.e., ConservationProblem) object.
Object (i.e., ConservationProblem) with the decisions added
to it.
See decisions for an overview of all functions for adding decisions.
Other decisions:
add_binary_decisions(),
add_proportion_decisions(),
add_semicontinuous_decisions()