Add Cumulative Incidence Function Calculation to the Exit Modeler

[jay-dennis]

A key item of interest desired from use of the Exit Modeler is the Cumulative Incidence Function (CIF). Currently the CIF must be pieced together from Survival and Exit Forecasts. We show how to do this in the documentation. This calculation should be automatic, and can be easily implemented. Code for doing this can be found in the feature/CIF branch and will be incorporated into FIFE's Exit Modeler.