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

plugins/slack/server/.babelrc

@@ -0,0 +1,3 @@
+{ 
+  "extends": "../../../server/.babelrc"
+}