Enhancements for sample estimation - response rate and sampling

[quillan86]

Currently there isn't a way to account for response rate in the stratified sampling estimate per strata(the interface is there but not the functionality; tested it during the AAPOR meeting). I'd like to account for the individual strata in response rate and perhaps do this in a bit more flexible manner if possible. This will allow our team to use this for our sampling plan - we stratify by geographical region and the response rates which we have historical data on differ by region.