PLT-2555/PLT-5009/PLT-5225 Changed system messages to be rendered by the client (#5209)

* Moved rendering of (message deleted) into PostMessageView

* Added additional post types to constants on client

* Changed system messages to be rendered in the client's language

* Updated new system messages to have relevant usernames highlighted and have markdown rendered in header change messages

webapp/stores/notification_store.jsx

@@ -6,7 +6,6 @@ import EventEmitter from 'events';
 import Constants from 'utils/constants.jsx';
 import UserStore from './user_store.jsx';
 import ChannelStore from './channel_store.jsx';
-import PreferenceStore from './preference_store.jsx';
 import * as UserAgent from 'utils/user_agent.jsx';
 import * as Utils from 'utils/utils.jsx';
 import * as PostUtils from 'utils/post_utils.jsx';
@@ -35,8 +34,6 @@ class NotificationStoreClass extends EventEmitter {
         if ((UserStore.getCurrentId() !== post.user_id || post.props.from_webhook === 'true')) {
             if (PostUtils.isSystemMessage(post)) {
                 return;
-            } else if (!PreferenceStore.getBool(Constants.Preferences.CATEGORY_ADVANCED_SETTINGS, 'join_leave', true) && post.type === Constants.POST_TYPE_JOIN_LEAVE) {
-                return;
             }
 
             let mentions = [];

webapp/stores/post_store.jsx

@@ -8,7 +8,7 @@ import ChannelStore from 'stores/channel_store.jsx';
 import BrowserStore from 'stores/browser_store.jsx';
 import UserStore from 'stores/user_store.jsx';
 
-import Constants from 'utils/constants.jsx';
+import {Constants, PostTypes} from 'utils/constants.jsx';
 const ActionTypes = Constants.ActionTypes;
 
 const CHANGE_EVENT = 'change';
@@ -616,7 +616,9 @@ class PostStoreClass extends EventEmitter {
 
         if (!joinLeave && postsList) {
             postsList.order = postsList.order.filter((id) => {
-                if (postsList.posts[id].type === Constants.POST_TYPE_JOIN_LEAVE) {
+                const post = postsList.posts[id];
+
+                if (post.type === PostTypes.JOIN_LEAVE || post.type === PostTypes.JOIN_CHANNEL || post.type === PostTypes.LEAVE_CHANNEL) {
                     Reflect.deleteProperty(postsList.posts, id);
 
                     return false;