Ultimate Member - Private Messages 2.3.9

* Fixed: Loading assets in block builder
* Fixed: Send button enabled after the limit is exceeded and deleting extra characters
* Tweak: Added Ultimate Member as required plugins

2.3.7

* Added: Option for hide message button for guests
* Fixed: PHP warnings
* Fixed: Removed `extract()`
* Fixed: Issue with lack of the nonces
* Fixed: "editable" field data format in predefined fields
* Tweak: Template overwrite versioning
* Tweak: changed `input_filter` to WordPress native sanitize
* Tweak: Ultimate Member 2.6.7 compatibility