Unlock Jinja2 2.8.1

[tulimaki]

Front app is now locked to jinja2 2.8.1 since the complex inheritance with macros.

Now front extends those macros here like this
{% extends "shuup/front/macros/theme/navigation.jinja" %}

And what this could be is that this file has the customized macros and that “extends” are for default/fallback macros and each macro would have “if exists” wrapped around it. At least this solution would still allow overriding single macros from default front for customized themes.

The current front app works but after updating 2.9.0 you can reproduce this easily by checking the classic gray menu extension.