Ability to solve ACOPF with a modified network topology

[vishwas1984]

Currently we can solve the ACOPF with standard network topologies (such as 9-bus, 118-bus etc). It would be useful to be able to solve ACOPF with a modified network topology -- (for example, the ability to solve a 9-bus system with a line removed or a generator removed). I think all the infrastructure is there -- and I think by adding an additional input to ProxALEvaluator will facilitate this.

[AnirudhSubramanyam]

We need to implement generator contingencies as well @vishwas1984 @michel2323. One easy way to do this is by setting its active and reactive power generation limits to 0.