Allow Maniphest queries to have configurable page sizes

Summary:
Current page size is `1000`. This is nice to have in some cases, but makes pages slower than necessary in others. Task lists are generally dominated by rendering costs.

For example, my default is "recent tasks", which just lists all tasks ordered by date created. Showing 100 tasks here instead of 1000 makes this several times faster without compromising utility.

I don't want to force the default to 100, though, since sometimes listing everything is quite useful and I think an advantage of Maniphest is that it generally deals reasonably well with large task sets.

(This `limit` property is actually read by the default implementation of `getPageSize()` in the parent class.)

Test Plan: Made queries with page sizes 1, 100, 12, 9, 3000, etc.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6976

src/applications/maniphest/query/ManiphestTaskSearchEngine.php

@@ -57,6 +57,11 @@ final class ManiphestTaskSearchEngine
     $saved->setParameter('createdStart', $request->getStr('createdStart'));
     $saved->setParameter('createdEnd', $request->getStr('createdEnd'));
 
+    $limit = $request->getInt('limit');
+    if ($limit > 0) {
+      $saved->setParameter('limit', $limit);
+    }
+
     return $saved;
   }
 
@@ -310,6 +315,13 @@ final class ManiphestTaskSearchEngine
       pht('Created After'),
       'createdEnd',
       pht('Created Before'));
+
+    $form
+      ->appendChild(
+        id(new AphrontFormTextControl())
+          ->setName('limit')
+          ->setLabel(pht('Page Size'))
+          ->setValue($saved->getParameter('limit', 100)));
   }
 
   protected function getURI($path) {