Update bookmark form with proper bootstrap markup

src/templates/chatroom_bookmark_form.html

 <div class="chatroom-form-container">
     <form class="converse-form chatroom-form">
-        <fieldset class="form-group">
         <legend>{{{o.heading}}}</legend>
-            <label>{{{o.label_name}}}</label>
-            <input type="text" name="name" required="required"/>
-            <label>{{{o.label_autojoin}}}</label>
-            <input type="checkbox" name="autojoin"/>
-            <label>{{{o.label_nick}}}</label>
-            <input type="text" name="nick" value="{{{o.default_nick}}}"/>
+        <fieldset class="form-group">
+            <label for="converse_muc_bookmark_name">{{{o.label_name}}}</label>
+            <input class="form-control" type="text" name="name" required="required" id="converse_muc_bookmark_name"/>
+        </fieldset>
+        <fieldset class="form-group">
+            <label for="converse_muc_bookmark_nick">{{{o.label_nick}}}</label>
+            <input class="form-control" type="text" name="nick" value="{{{o.default_nick}}}" id="converse_muc_bookmark_nick"/>
+        </fieldset>
+        <fieldset class="form-group form-check">
+            <input class="form-check-input" id="converse_muc_bookmark_autojoin" type="checkbox" name="autojoin"/>
+            <label class="form-check-label" for="converse_muc_bookmark_autojoin">{{{o.label_autojoin}}}</label>
         </fieldset>
         <fieldset class="form-group">
             <input class="btn btn-primary" type="submit" value="{{{o.label_submit}}}"/>