Performance: Inbox Paging / loading (#11157)

* load messages per conversation

* only sort ones in ui

*  add contributor to message

* fix correct message layout/message

* mugenScroll on chatMessages

* fix lint, no mugen-scroll, use own scroll handler

* fix height / margin of modal + use button to load more

* fix tests

* user data from inbox

* style "load earlier messages"

*  move mapMessage to the inbox api result / extract sentMessage of members-api-controller

* fix test back

* fix test

* keep last scroll position

* just set the Id of the returned message instead of all other properties

* fix add new messages (buttons were hidden) + load more

* item-mounted debounce to trigger the re-scrolling

test/api/v3/integration/inbox/GET-inbox_messages.test.js

@@ -6,7 +6,7 @@ describe('GET /inbox/messages', () => {
   let user;
   let otherUser;
 
-  before(async () => {
+  beforeEach(async () => {
     [user, otherUser] = await Promise.all([generateUser(), generateUser()]);
 
     await otherUser.post('/members/send-private-message', {