New fields: M_.ramsey_orig_{eq,endo}_nbr

– M_.ramsey_orig_endo_nbr is the number of endogenous variables in the model
  present just before adding the Lagrange multipliers and computing the Ramsey
  FOC; it is by construction equal to the number of equations that will be added
  by the process of computing the FOCs
– M_.ramsey_orig_eq_nbr is the number of equations in the model present just
  before adding the Lagrange multipliers and computing the Ramsey FOC; it is by
  construction equal to the number of Lagrange multipliers that will be added by
  the process of computing the FOCs

Note that both may be greater than the number of endogenous/equations written
by the user, because some auxiliary variables may have already been added.

Also note that the number of policy instruments in M_.ramsey_orig_endo_nbr −
M_.ramsey_orig_eq_nbr

As a consequence, drop M_.ramsey_eq_nbr (which was actually equal to
M_.ramsey_orig_endo_nbr) and M_.orig_eq_nbr (which was actually equal to
M_.ramsey_orig_eq_nbr, but would also be set in the non-Ramsey case). The new
names are clearer.