* fix: removed duplicate checkContent call in addMessage
addMessage is called in one place (sendMessage), and the checks
are already contained there. addMessage is the lower level call
and so should be called only from within core itself.
* feat: #7330 chat system messages for join, leave, rename
* fix: add back content checking in .addMessage();
* fix: tests, and added .addSystemMessage() method
Tests were relying on message indices that changed due to the
new system messages.
* feat: add tests for system chat messages
* refactor: rewrite half of src/messaging/rooms.js, fix tests
* feat: #7743 messaging/room.js
* fix: tests for messaging/room.js, #7743
* fix: trying to fix tests
* fix: omg :rage2:
4fb271c684