#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

api/admin.py

@@ -0,0 +1,16 @@
+from django.contrib import admin
+
+from api.models.token import APIUserToken
+
+
+class APITokenAdmin(admin.ModelAdmin):
+    list_display = [
+        "token",
+        "valid_until",
+        "is_active",
+    ]
+    readonly_fields = [
+        "token"
+    ]
+
+admin.site.register(APIUserToken, APITokenAdmin)