PLT-1750 Moved slash commands to backstage

* Added slash commands to InstalledIntegrations page

* Reset installed integration type filter if there is no longer any integrations of the selected type

* Added pages to backstage to add slash commands

* Cleaned up internationalization for slash commands

* Added ability to regen slash command tokens from backstage

* Removed Integrations tab from UserSettings

webapp/utils/constants.jsx

@@ -78,6 +78,10 @@ export default {
         RECEIVED_OUTGOING_WEBHOOK: null,
         UPDATED_OUTGOING_WEBHOOK: null,
         REMOVED_OUTGOING_WEBHOOK: null,
+        RECEIVED_COMMANDS: null,
+        RECEIVED_COMMAND: null,
+        UPDATED_COMMAND: null,
+        REMOVED_COMMAND: null,
 
         RECEIVED_MSG: null,