Detect when devices and branches are disconnected when output results.

[rodrigomha]

Currently, when a Line is tripped and the current or power is requested in the output solution, the result will not output zero, since it does not know that the line was tripped.

Possible solution: Make line unavailable when is tripped in the Callback. Then check in some form that the line is unavailable when requested the output. This will not know WHEN the line was tripped.

General problem: We need a way to store when a load or line is tripped, such that if the user wants to see the power of the solution, that is computed using algebraic values, properly output the value until is tripped (and then output zero).