Reorganize Chat component files

- MessageList renamed to RoomEventList
- MessageDelegate renamed to RoomEventDelegate
- Banner and RoomEventList get their own folders

harmonyqml/components/Chat/Chat.qml

@@ -1,6 +1,8 @@
 import QtQuick 2.7
 import QtQuick.Controls 2.2
 import QtQuick.Layouts 1.4
+import "Banners"
+import "RoomEventList"
 
 ColumnLayout {
     property string userId: ""
@@ -22,7 +24,7 @@ ColumnLayout {
         topic: roomInfo.topic
     }
 
-    MessageList {}
+    RoomEventList {}
 
     TypingUsersBar {}