Allow Herald rules to be disabled, instead of deleted

Summary:
Ref T603. Ref T1279. Further improves transaction and policy support for Herald.

  - Instead of deleting rules (which wipes out history and can't be undone) allow them to be disabled.
  - Track disables with transactions.
  - Gate disables with policy controls.
  - Show policy and status information in the headers.
  - Show transaction history on rule detail screens.
  - Remove the delete controller.
  - Support disabled queries in the ApplicationSearch.

Test Plan:
  - Enabled and disabled rules.
  - Searched for enabled/disabled rules.
  - Verified disabled rules don't activate.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1279, T603

Differential Revision: https://secure.phabricator.com/D7247

src/applications/search/engine/PhabricatorApplicationSearchEngine.php

@@ -299,6 +299,25 @@ abstract class PhabricatorApplicationSearchEngine {
   }
 
 
+  protected function readBoolFromRequest(
+    AphrontRequest $request,
+    $key) {
+    if (!strlen($request->getStr($key))) {
+      return null;
+    }
+    return $request->getBool($key);
+  }
+
+
+  protected function getBoolFromQuery(PhabricatorSavedQuery $query, $key) {
+    $value = $query->getParameter($key);
+    if ($value === null) {
+      return $value;
+    }
+    return $value ? 'true' : 'false';
+  }
+
+
 /* -(  Dates  )-------------------------------------------------------------- */