users: Use checkboxes for groups during create

plinth/modules/users/forms.py

@@ -41,6 +41,7 @@ class CreateUserForm(UserCreationForm):
         choices=GROUP_CHOICES,
         label=_('Groups'),
         required=False,
+        widget=forms.CheckboxSelectMultiple,
         help_text=_('Select which services should be available to the new '
                     'user. The user will be able to log in to services that '
                     'support single sign-on through LDAP, if they are in the '

plinth/modules/users/templates/users_create.html

@@ -20,6 +20,14 @@
 
 {% load bootstrap %}
 
+{% block page_head %}
+  <style type="text/css">
+    .multiple-checkbox li {
+      list-style-type: none;
+    }
+  </style>
+{% endblock %}
+
 {% block content %}
 
   <div class="row">