Update custom fields opencart 2.0.x.x to 2.x.x.x

What it does:
- Converts to serialize database data to json opencart the 2.0.x.x to be compatible with versions 2.1.x.x or 2.2.x.x;

Installation / Installation:
- Simple installation because it uses the native OCMOD extensions installer in store opencart

Compatibility / Compatibility:
- 2.1.x.x