Adds commands to Yargs

@param yargs {yargs} the Yargs instance
@param classNames {String[]} array of class names, each of which is in the `packageName` package
@param packageName {String} the name of the package to find each command class
function(yargs, classNames, packageName) {
      let pkg = null;
      packageName.split(".").forEach(seg => {
        if (pkg === null) {
          pkg = window[seg];
        } else {
          pkg = pkg[seg];
        }
      });
      classNames.forEach(cmd => {
        require("../../../" + packageName.replace(/\./g, "/") + "/" + cmd);
        let data = pkg[cmd].getYargsCommand();
        yargs.command(data);
      });
    }