Implement batch downloading of single audit PDFs

[fureigh]

User story

As an agency representative using this system, I want my search to yield all relevant single audits, not just the first 100, so that I can trust and make best use of these results.

Acceptance criteria

• [x] When a search yields results (not FAC's "too many results" page), this system downloads all single audit PDFs that were included in the search results, even when there are more than 100 results.

Outstanding questions

None at the moment.

Implementation notes

• The current download limit is 100. However, the interface provides a way to select 100 at a time. Plan to iterate through the options presented in the dropdown, downloading each in sequence.
• There's room to present the results more elegantly, but the minimum viable output would be a set of ZIP files containing up to 100 PDFs each.
• ~Address form downloads (as distinct from PDF downloads) in a separate issue/ticket.~ (Update: addressed on 8/28/2019 in https://github.com/18F/federal-grant-reporting/issues/149.)

[fureigh]

No longer seeing relevant options in the drop-down, oddly, so try this instead:

<tr class="GridPager">
  <td colspan="11"><table>
   <tr>
   <td><span>1</span></td>
   <td><a href="javascript:__doPostBack(&#39;ctl00$MainContent$ucA133SearchResults$ResultsGrid&#39;,&#39;Page$2&#39;)">2</a></td>
   <td><a href="javascript:__doPostBack(&#39;ctl00$MainContent$ucA133SearchResults$ResultsGrid&#39;,&#39;Page$3&#39;)">3</a></td>
   </tr>
   </table></td>
</tr>

Corresponding visual element:

Corresponding visual element in context: