Plugin architecture (#4861)

* wip

* Refactor, tasks, processors, routes loading

* Move Slack settings config to plugin

* Fix translations in plugins

* Move Slack auth to plugin

* test

* Move other slack-related files into plugin

* Forgot to save

* refactor

shared/utils/routeHelpers.ts

@@ -0,0 +1,7 @@
+export function signin(service = "slack"): string {
+  return `/auth/${service}`;
+}
+
+export function integrationSettingsPath(id: string): string {
+  return `/settings/integrations/${id}`;
+}