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