chore: Refactor backlinks and revisions (#1611)

* Update backlinks service to not rely on revisions

* fix: Add missing index for finding backlinks

* Debounce revision creation (#1616)

* refactor debounce logic to service

* Debounce slack notification

* Revisions created by service

* fix: Revision sidebar latest

* test: Add tests for notifications

server/migrations/20201028043021-reverse-document-id-index.js

@@ -0,0 +1,11 @@
+'use strict';
+
+module.exports = {
+  up: async (queryInterface, Sequelize) => {
+    await queryInterface.addIndex("backlinks", ["reverseDocumentId"]);
+  },
+
+  down: async (queryInterface, Sequelize) => {
+    await queryInterface.removeIndex("backlinks", ["reverseDocumentId"]);
+  }
+};