Interpolate Yearly Cashflow

[dcolleoni]

1. Provide entry point to define the CF timestep. (Monthly = Default, Quarterly, Yearly - can this be a SingleDataNodeParameter?)
2. Provide entry point to define how to interpolate the provided CF to match the monthly timestep. (Uniform, others - can this be a SingleDataNodeParameter?)
3. Interpolate the CF to monthly timestep.