Ninja Forms - File Uploads Addon 3.3.22

*Bugs:*
* Fix mergetags variations not rendering the correct value
* Fix external file url redirecting to site admin home if the service is no longer connected

*New:*

* Button to cancel a file upload, or clear an error after a failed upload

*Bugs:*

* File upload links being stripped from emails and success messages
* Fatal error when uploading multiple files to Google Drive and renaming the file names
* Required field validation error shows when the 'Select Files' button clicked
* Missing file upload when submitting a form that had previously been saved with the Save Progress addon
* Multiple file upload URLs appearing as one large broken link in emails
* PHP notices about mergetag values when saving a form
* Browse uploads table losing form filter when paginating or sorting

*Bugs:*

* Some large files corrupted when uploading to Dropbox
* Error not displayed when uploading a file larger than the maximum defined in settings
* Fix PHP Notice: Undefined variable: mime_types_whitelist

*Changes:*

* Added new filter 'ninja_forms_uploads_tmp_dir' to change the temp directory for uploads
* Added external service $slug parameter to the filter 'ninja_forms_uploads_should_background_upload'