OpenCart 2 compatibility

[wojtek-willows]

The code is not compatible with OpenCart 2, Twig was only introduced in OC3.

[marekgach]

Thank you @wojtek-willows for a report. I will need to take a deeper look. I tested the plugin on our staging CMS - OC 3.0.2.0 and OC 2.3.0.2 and everything is working.

We will try to test installation on OC 3.0.3 and version OC 2.3 once again.