UI: Show loader icon on messages page while messages got rendered for the first time

[MihanEntalpo]

When the clipboard page opens, before the messages have been rendered - it is necessary to display the loader spinner, if there are no messages - write "no messages yet"

Also, messages are now only rendered for the first time after the first successful fetch of the list of unread messages from the server, although the messages may well already be in the browser by the time they are downloaded.