code: function getAllEntries(groups) {
      return groups.reduce(function(current, group) {
          const theseEntries = group.getEntries();
          const subEntries = getAllEntries(group.getGroups());
          if (theseEntries.length > 0) {
              current = current.concat(theseEntries);
          }
          if (subEntries.length > 0) {
              current = current.concat(subEntries);
          }
          return current;
      }, []);
  }
docs: Get all entries within a collection of groups
  @param {Array.<Group>} groups An array of groups
  @returns {Array.<Entry>} An array of entries