Make `byName` work with `uniquePopulationName`

[zbjornson]

From Federico Gherardini

There's no way to do this from the API currently. A helper function to do this client-side:

getPopByUniqueName <- function(uniqueName) {
  myPops <- getPopulations(experimentId)
  myPops[myPops$uniqueName %in% uniqueName,]
}