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

app/typings/window.d.ts

@@ -1,4 +1,13 @@
 declare global {
+  interface NodeRequire {
+    /** A special feature supported by webpack's compiler that allows you to get all matching modules starting from some base directory.  */
+    context: (
+      directory: string,
+      useSubdirectories: boolean,
+      regExp: RegExp
+    ) => any;
+  }
+
   interface Window {
     dataLayer: any[];
     gtag: (...args: any[]) => void;