Tests: add test project

* manage.py file at the root of the project
* targetting the project located at tests/test_project/settings.py

That allows testing the linter through just calling it on the project itself.
Using the new method coming soon: `python manage.py lintmigrations`

tests/test_project/urls.py

@@ -0,0 +1,19 @@
+"""test_project URL Configuration
+
+The `urlpatterns` list routes URLs to views. For more information please see:
+    https://docs.djangoproject.com/en/2.1/topics/http/urls/
+Examples:
+Function views
+    1. Add an import:  from my_app import views
+    2. Add a URL to urlpatterns:  path('', views.home, name='home')
+Class-based views
+    1. Add an import:  from other_app.views import Home
+    2. Add a URL to urlpatterns:  path('', Home.as_view(), name='home')
+Including another URLconf
+    1. Import the include() function: from django.urls import include, path
+    2. Add a URL to urlpatterns:  path('blog/', include('blog.urls'))
+"""
+from django.contrib import admin
+from django.conf.urls import url
+
+urlpatterns = [url("admin/", admin.site.urls)]