Create new zip exporter for handling multiple individuals.

[kaladay]

The is part of issue TAMULib/scholars-angular#337 .

Using the existing exporters and selecting zip, such as the example code below, results in an error about this not being supported.

      String testQ = "(id:n0016a660 OR id:n54c59a01)^=1.0 AND class:\"Person\"";
      QueryArg query = QueryArg.of(Optional.of(testQ), empty(), empty(), empty(), empty(), empty());
      List<FilterArg> filters = new ArrayList<>();
      List<BoostArg> boosts = new ArrayList<>();
      List<ExportArg> export = new ArrayList<>();

      Exporter exporter = exporterRegistry.getExporter("zip");
      return ResponseEntity.ok()
          .header(CONTENT_DISPOSITION, exporter.contentDisposition(normalizeExportFilename("example")))
          .header(CONTENT_TYPE, exporter.contentType())
          .body(exporter.streamIndividuals(repo.export(query, filters, boosts, Sort.unsorted()), export));

The ability to use

Implementing exporters other than zip might be a good idea but should be considered out of scope of this issue.
Only if it is convenient and simple should the others be implemented.

The csv appears to support this, but it may or may not need more work.

This issue is only about implementing the zip exporter for multiple individuals and is not about any other task.