Fix some small bugs
[Notes] Bugfix: next pages do not load properly
Bugfix: chat close button sometimes does not work properly
Show unread chat messages in Notification Center on page reload
Only blinking chat window if it has unread messages
Remove all system messages without comments from News Feed
Remember chatbox state (expand or collapse) when page reload
Bugfix: Seen by & typing status not working properly in group chat
Bugfix: Can't upload files (using upload button on chatbox title bar)