Correct tox deps and remove setup.cfg

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 skipsdist = True
 usedevelop = True
-isolated_build = True
+skip_missing_interpreters = True
 
 envlist = 
     py39-dj32-wt41-{sqlite,postgres,mysql}
@@ -21,22 +21,23 @@ DATABASE =
     mysql: mysql
 
 [testenv]
-skip_install = True
+install_command = pip install -e ".[testing]" -U {opts} {packages}
+
 commands = 
     coverage run manage.py test --deprecation all
     coverage report -m
 
 deps =
     coverage
 
-    django32: Django>=3.2,<4.0
-    django42: Django>=4.2,<4.3
-    django50: Django>=5.0,<5.1
+    dj32: Django>=3.2,<4.0
+    dj42: Django>=4.2,<4.3
+    dj50: Django>=5.0,<5.1
 
-    wagtail41: Wagtail>=4.1,<4.2
-    wagtail52: Wagtail>=5.2,<5.3
-    wagtail60: Wagtail>=6.0,<6.1
-    wagtail61: Wagtail>=6.1,<6.2
+    wt41: Wagtail>=4.1,<4.2
+    wt52: Wagtail>=5.2,<5.3
+    wt60: Wagtail>=6.0,<6.1
+    wt61: Wagtail>=6.1,<6.2
 
     postgres: psycopg2
     mysql: mysqlclient