#31 API basic implementation

* adds new app to project
* adds relation between User model and new APIUserToken model
* adds first implementation for GET of intervention
* adds basic code layout for future extension by having new versions

konova/urls.py

@@ -38,6 +38,7 @@ urlpatterns = [
     path('news/', include("news.urls")),
     path('cl/', include("codelist.urls")),
     path('analysis/', include("analysis.urls")),
+    path('api/', include("api.urls")),
 
     # Generic deadline routes
     path('deadline/<id>/remove', remove_deadline_view, name="deadline-remove"),