Add 'paste.query' conduit method and deprecate 'paste.info'

Summary:
  - Modernize the Paste Conduit API.
  - Deprecate 'paste.info'.
  - Make queries policy-aware.
  - Move methods into the application to support greater modularity.

Test Plan: Made `paste.query`, `paste.info`, `paste.create` calls. Browsed Paste interfaces. Forked a paste.

Reviewers: vrana, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3379

src/applications/paste/controller/PhabricatorPasteEditController.php

@@ -43,6 +43,7 @@ final class PhabricatorPasteEditController extends PhabricatorPasteController {
         $parent = id(new PhabricatorPasteQuery())
           ->setViewer($user)
           ->withIDs(array($parent_id))
+          ->needContent(true)
           ->execute();
         $parent = head($parent);
 
@@ -105,11 +106,7 @@ final class PhabricatorPasteEditController extends PhabricatorPasteController {
       if ($is_create && $parent) {
         $paste->setTitle('Fork of '.$parent->getFullName());
         $paste->setLanguage($parent->getLanguage());
-
-        $parent_file = id(new PhabricatorFile())->loadOneWhere(
-          'phid = %s',
-          $parent->getFilePHID());
-        $text = $parent_file->loadFileData();
+        $text = $parent->getContent();
       }
     }