Register theme prefixes as namespaces in twig

[WizKid]

When creating a theme that inherit from another theme one common thing is that you want to change a tiny thing in an existing twig file.

I couldn't find a good way to do that without copy the whole twig-file over to my theme. Which means that if the base theme update that twig-file I will never get the changes. And I couldn't figure out a way to reference the base theme twig file and override it at the same time.

So with this change I can change my theme config to something like this:

streams:
  schemes:
    theme:
      type: ReadOnlyStream
      prefixes:
        '':
          - user/themes/mytheme
          - user/themes/quark
        'quark/':
          - user/themes/quark

And then if I want to update the footer in base.html.twig I can just create a base.html.twig file in mytheme that looks something like this:

{% extends '@quark/partials/base.html.twig' %}

{% block footer %}
    My footer text
{% endblock %}

When I first implemented it I just had one foreach that handled the empty prefix also. But because when $this->grav->fireEvent('onTwigTemplatePaths'); some stuff goes in and touches $this->twig_paths that didn't work.

[rhukster]

This look good to me, let me discuss with @mahagr though...

[WizKid]

I mostly want some way to access the original template. Because that would make things so much easier. This was the easiest way I could figure out. So there may absolutely be some better way to do this.

[mahagr]

Change looks good to me.