Introduce "dev environment" and dotenv

There are now two dockerfiles. One for production, one for development.
All configuration is now also handled through dotenv files,
which these dotenv files, as well as the included VSCode launch tasks
use.

docker-compose.yml

@@ -0,0 +1,15 @@
+# This Compose file is for development only. It is not intended for production use.
+# It only starts auxiliary services, such as a database, that are required for the
+# application to run. The application itself is started separately, using the
+# command "python -m flask run" or your favorite IDE.
+# Useful for attaching a debugger to the application.
+
+version: "3.9"
+
+services:
+  db:
+    image: mariadb
+    restart: always
+    env_file: .env.dev
+    ports:
+      - "3306:3306"