Upgrade to Wagtail 2.7

requirements/base.txt

@@ -1,5 +1,5 @@
 Django>=2.2,<2.3
 django-dotenv==1.4.1
-wagtail>=2.6,<2.7
+wagtail>=2.7,<2.8
 wagtailfontawesome>=1.1.3,<1.2
 Pillow>=6.2.0,<6.3