API: Add experimental Json API

in preparation for external healthchecks and the
admin backend. We define a couple test routes:

- / List all routes
- /ping Replies pong for online-checks
- /stats Get high-level bot statistics
- /most-recent-drop Returns the most recent entry from dropHistories

The last two routes require a valid apikey header.
All routes are prefixed by /api/v1

docker-compose.yml

@@ -10,6 +10,8 @@ services:
     depends_on:
       - "mysql"
     working_dir: /app
+    ports:
+      - 127.0.0.1:${API_PORT}:${API_PORT}
     volumes:
       - ./:/app
       - /usr/share/fonts/:/usr/share/fonts/