templatetags: add utils template filters and tags

Add utils.py file to create template filters and tags that can be used
by most if not all objects in Patchwork. In particular, add a template
filter to get the plural verbose name of a model and add a template tag
that returns whether an object is editable by the current user. These
utilities will be used in an upcoming patch that adds the `addressed`
status label to patch and cover comments.

Signed-off-by: Raxel Gutierrez <raxel@google.com>
Reviewed-by: Stephen Finucane <stephen@that.guru>
Signed-off-by: Daniel Axtens <dja@axtens.net>

Author: Raxel Gutierrez

patchwork/templatetags/utils.py

@@ -0,0 +1,18 @@
+# Patchwork - automated patch tracking system
+# Copyright (C) 2021 Google LLC
+#
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+from django import template
+
+register = template.Library()
+
+
+@register.filter
+def verbose_name_plural(obj):
+    return obj._meta.verbose_name_plural
+
+
+@register.simple_tag
+def is_editable(obj, user):
+    return obj.is_editable(user)