Ultimate Member - Private Messages 2.3.9

* Fixed: Layout issues related to the textarea auto-size and the conversation layout
* Fixed: Security issue related to the COOKIES using

* Templates required update:
- conversation.php
- emoji.php
- message.php

* Cached and optimized/minified assets(JS/CSS) must be flushed/re-generated after upgrade

* Added: Refresh new real-time notifications on async query when conversation is refreshed

* Added: 'Hide a "Download Chats History" link' setting.
* Fixed: setCaretPosition when paste emoji in the message textarea
* Fixed: Extension settings structure
* Deprecated: user_id attribute for [ultimatemember_messages] shortcode. Messaging conversations list is displayed only for the current logged in user