LearnDash LMS Gravity Forms Integration Addon 2.1.3

* Updated improve LD GF select2 box styling
* Updated add horizontal padding to LD option input field
* Updated improve style of LD options select box in GF field choices
* Updated use entry form feed setting to make its filter hook works instead of pulling feed settings from DB
* Fixed editor CSS styles are broken because of jQuery UI base theme CSS
* Fixed undefined array index error
* Fixed incorrect property name is JS script
* Fixed JS conflict error on form edit screen
* Fixed selecting options in LD options select box for GF field choices close GF choices UI flyout

* Added ability to assign a LearnDash group
* Added allow conditional group enrollment based upon a form input
* Added ability to support Gravity Forms conditonal logic
* Fixed PHP notice
* Fixed users not being enrolled when a Stripe payment field is part of the form

* Added payment refunded hooked function for paid form
* Added payment completed hooked function for paid form
* Added logic to bail course enrollment in user registration hook if the submitted form is a paid form
* Added paid form setting field to mark a paid form on user registration feed setting

Fixed internal server error due to an undefined variable