Add inline_admin_formset associated classes

[marcoooo]

Hi, I just run into this (little issue): il you use Django 1.10 and add a SortableMixin with TabularInline, you will loose the classes elements associated with inline classes definition (such as collapse functionnality).

You may correct this very simply modifying templates/adminsortable2/tabular.html
replacing :

<div class="inline-group sortable" id="{{ inline_admin_formset.formset.prefix }}-group">
  <div class="tabular inline-related {% if forloop.last %}last-related{% endif %}">
{{ inline_admin_formset.formset.management_form }}
<fieldset class="module">
   <h2>{{ inline_admin_formset.opts.verbose_name_plural|capfirst }}</h2>
   {{ inline_admin_formset.formset.non_form_errors }}
   <table>
     <thead><tr><th>{% trans "Sort" %}</th>

with

{% load i18n admin_urls admin_static admin_modify %}
<div class="inline-group sortable" id="{{ inline_admin_formset.formset.prefix }}-group">
  <div class="tabular inline-related {% if forloop.last %}last-related{% endif %}">
{{ inline_admin_formset.formset.management_form }}
<fieldset class="module **{{ inline_admin_formset.classes }}**">
   <h2>{{ inline_admin_formset.opts.verbose_name_plural|capfirst }}</h2>
   {{ inline_admin_formset.formset.non_form_errors }}
   <table>

Would you like a PR ?
M.

[jrief]

sorry for now answering in time.
Yes a pull request would be nice.