Jacobian formulation for all buses

[rbolgaryn]

Having the Jacobian matrix with 2 values per bus, regardless of bus type (PV, PQ, REF) would allow only 1 symbolic factorization, and only using numerical factorizations for consecutive NR calculations (for PV->PQ transformation NR runs, and for different time steps).

The values of F will be 0 for the not relevant bus values