Allow to generate QR code for short URLs in page edit screen

[norbertlaposa]

• create new file controllers/bo/component/qr_code.php
• add https://github.com/chillerlan/php-qrcode via composer in onyx folder (not project specific composer.json)
• add input validation for GET parameters string url (base64 endcoded URL) and format (png or pdf)
• save each file generated to var folder, for example /var/qr-code/aHR0cHM6Ly9jZW50cmEuaWUvOTk1IC1uCg==.png
• display QR code in backoffice via new templates/bo/node/item_qr_code.html where will be a button to call /request/bo/component/qr_code=url=aHR0cHM6Ly9jZW50cmEuaWUvOTk1IC1uCg==&format=png
• allow to download PNG via standard download controller, e.g <image src="/download/var/qr-code/aHR0cHM6Ly9jZW50cmEuaWUvOTk1IC1uCg==.png" />