Update CSV processing in estimateBiomass similar to plotSurvey

[kstierhoff]

Updated CSV processing to detect changed/added files with the snapshot method akin to that used in plotSurvey.

[kstierhoff]

Also make a generic script that processes CSV files for other tools that don't rely on estimateBiomass, for example. Consult @jrenfree for other needs.