WP File Download - Joomunited 6.1.6

* Fix : Missing files when using the preview theme
* Fix : Upload folder in admin is incorrect in some cases

* Add : Possibility to upload folder on Frontend
* Fix : Wrong pagination on frontend
* Fix : PHP warning

* Add : Email notification system: Support notify email per category
* Add : Email notification system: Support file download URL tag for custom email content
* Add : Email notification system: Support file upload date tag for custom email content
* Fix : Default layout theme issue
* Fix : Tree theme breadcrumbs issue
* Fix : PHP warning on frontend