Add new Trove Classifiers for Python 3 only, Wagtail, and Django.

setup.py

@@ -29,6 +29,11 @@ setup(
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3 :: Only',
+        'Framework :: Django',
+        'Framework :: Django :: 2.0',
+        'Framework :: Wagtail',
+        'Framework :: Wagtail :: 2',
         'Topic :: Internet :: WWW/HTTP',
         'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
         'Topic :: Internet :: WWW/HTTP :: Site Management',