Ultimate Member - Private Messages 2.3.9

* Fixed: Conversation block's horizontal scroll
* Tweak: jQuery v3 compatibility

* Added: `count_messages` method
* Added: CSS for messages button at the profile page
* Added: 3rd party settings integration hook
* Fixed: Typo shortcode on the messages profile tab
* Fixed: Security vulnerability with getting conversations content
* Fixed: URL including `#` links
* Fixed: `limit_reached` method

* Added: The default value for attribute "user_id" of the shortcode [ultimatemember_message_button]
* Added: *.pot translations file
* Added: CSS for messages button at the profile page
* Added: 3rd party integrations hook in settings section
* Fixed: Security vulnerability with getting conversations content
* Fixed: Modal Login form with reCAPTCHA
* Fixed: Modal windows links
* Fixed: URLs with # symbol
* Tweak: apply_shortcodes() function support