[Bug fix][Enhance] Songlist parser & Bunder version error message

- For Arcaea 5.5.8 (no test)
- New character "Ai-chan"
- Add a small tool to send error message
- A `songlist` parser problem #156
- Fix that header checker of bundle version gives incorrect error messages.

tools/server_maintenance.py

@@ -0,0 +1,19 @@
+from flask import Flask, jsonify
+
+app = Flask(__name__)
+
+HOST = '0.0.0.0'
+PORT = '80'
+
+@app.route('/favicon.ico', methods=['GET'])
+def favicon():
+    return ''
+
+@app.route('/<path:p>')
+def hello(p):
+    r = {"success": False, "error_code": 2}
+    return jsonify(r)
+
+
+if __name__ == '__main__':
+    app.run(host=HOST, port=PORT)