feat(room list): improve hover and selection style

Author: florianduros

res/css/views/rooms/RoomListPanel/_RoomListItemView.pcss

@@ -33,6 +33,7 @@
         flex: 1;
         height: 100%;
         overflow: hidden;
+        border-radius: 8px;
 
         .mx_RoomListItemView_content {
             height: 100%;