perfect_foresight_with_expectation_errors_{setup,solver}: streamline handling of guess values

– Remove the terminal_steady_state_as_guess_value option to pfwee_solver
– pfwee_setup now sets the same guess values as pf_setup (i.e. terminal steady
  state at all periods)
– With constant_simulation_length option, pfwee_solver uses terminal steady
  state as guess values for periods that are added to the simulation