allow importnimja to overwrite "context"

[enthus1ast]

This feature should enable importnimja to
make variables available to the imported template with a different name.

something like this:

{% importnimja "someTemplate.nimja" record = someList %}

twig syntax:

{% include 'template.html' with {'foo': 'bar'} %}

basically the same as compileTemplateStr and compileTemplateFile