Fix: when closing a modal the overlay doesn't get removed

Looks like the `webkitTransitionEnd` event doesn't fire because `fade`
is already on the modal, so there's no transition, which means that in
bootstrap.native the event doesn't get fired to remove the overlay.

src/converse-modal.js

@@ -31,11 +31,6 @@ converse.plugins.add('converse-modal', {
                         this.trigger_el.classList.remove('selected');
                     }
                 }, false);
-
-                // XXX: Workaround for an apparent Bootstrap.Native bug, where
-                // the 'fade' class isn't removed after closing the modal,
-                // causing it to flash-close when you open it again.
-                this.el.addEventListener('shown.bs.modal', () => u.removeClass('fade', this.el), false);
             },
 
             insertIntoDOM () {

src/templates/add_chatroom_modal.html

-<div class="modal fade" id="add-chatroom-modal" tabindex="-1" role="dialog" aria-labelledby="add-chatroom-modal-label" aria-hidden="true">
+<div class="modal" id="add-chatroom-modal" tabindex="-1" role="dialog" aria-labelledby="add-chatroom-modal-label" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">

src/templates/add_contact_modal.html

 <!-- Add contact Modal -->
-<div class="modal fade" id="add-contact-modal" tabindex="-1" role="dialog" aria-labelledby="addContactModalLabel" aria-hidden="true">
+<div class="modal" id="add-contact-modal" tabindex="-1" role="dialog" aria-labelledby="addContactModalLabel" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">

src/templates/chat_status_modal.html

 <!-- Change status Modal -->
-<div class="modal fade" id="modal-status-change" tabindex="-1" role="dialog" aria-labelledby="changeStatusModalLabel" aria-hidden="true">
+<div class="modal" id="modal-status-change" tabindex="-1" role="dialog" aria-labelledby="changeStatusModalLabel" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">

src/templates/chatroom_details_modal.html

-<div class="modal fade" id="room-details-modal" tabindex="-1" role="dialog" aria-labelledby="room-details-modal-label" aria-hidden="true">
+<div class="modal" id="room-details-modal" tabindex="-1" role="dialog" aria-labelledby="room-details-modal-label" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">

src/templates/chatroom_registration_modal.html

-<div class="modal fade" id="room-registration-modal" tabindex="-1" role="dialog" aria-labelledby="room-registration-modal-label" aria-hidden="true">
+<div class="modal" id="room-registration-modal" tabindex="-1" role="dialog" aria-labelledby="room-registration-modal-label" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">

src/templates/client_info_modal.html

 <!-- Change status Modal -->
-<div class="modal fade" id="modal-status-change" tabindex="-1" role="dialog" aria-labelledby="changeStatusModalLabel" aria-hidden="true">
+<div class="modal" id="modal-status-change" tabindex="-1" role="dialog" aria-labelledby="changeStatusModalLabel" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">

src/templates/list_chatrooms_modal.html

-<div class="modal fade" id="list-chatrooms-modal" tabindex="-1" role="dialog" aria-labelledby="list-chatrooms-modal-label" aria-hidden="true">
+<div class="modal" id="list-chatrooms-modal" tabindex="-1" role="dialog" aria-labelledby="list-chatrooms-modal-label" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">

src/templates/message_versions_modal.html

-<div class="modal fade" id="message-versions-modal" tabindex="-1" role="dialog" aria-labelledby="message-versions-modal-label" aria-hidden="true">
+<div class="modal" id="message-versions-modal" tabindex="-1" role="dialog" aria-labelledby="message-versions-modal-label" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">

src/templates/profile_modal.html

-<div class="modal fade" id="user-profile-modal" tabindex="-1" role="dialog" aria-labelledby="user-profile-modal-label" aria-hidden="true">
+<div class="modal" id="user-profile-modal" tabindex="-1" role="dialog" aria-labelledby="user-profile-modal-label" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">
@@ -17,7 +17,7 @@
                 </ul>
                 {[ } ]}
                 <div class="tab-content">
-                    <div class="tab-pane fade show active" id="profile-tabpanel" role="tabpanel" aria-labelledby="profile-tab">
+                    <div class="tab-pane active" id="profile-tabpanel" role="tabpanel" aria-labelledby="profile-tab">
                         <form class="converse-form converse-form--modal profile-form" action="#">
                             <div class="row">
                                 <div class="col-auto">
@@ -66,7 +66,7 @@
                         </form>
                     </div>
                     {[ if (o._converse.pluggable.plugins['converse-omemo'].enabled(o._converse)) { ]}
-                        <div class="tab-pane fade" id="omemo-tabpanel" role="tabpanel" aria-labelledby="omemo-tab">
+                        <div class="tab-pane" id="omemo-tabpanel" role="tabpanel" aria-labelledby="omemo-tab">
                             <form class="converse-form fingerprint-removal">
                                 <ul class="list-group fingerprints">
                                     <li class="list-group-item active">{{{o.__("This device's OMEMO fingerprint")}}}</li>

src/templates/user_details_modal.html

-<div class="modal fade" id="user-details-modal" tabindex="-1" role="dialog" aria-labelledby="user-details-modal-label" aria-hidden="true">
+<div class="modal" id="user-details-modal" tabindex="-1" role="dialog" aria-labelledby="user-details-modal-label" aria-hidden="true">
     <div class="modal-dialog" role="document">
         <div class="modal-content">
             <div class="modal-header">