refactor and get ready for offline compressing

Dynamically choosing static files and pre-compressing is not compatible, because it depends on data from the request to know the file name.

The way this is usually solved (with django-compressor) is to create a partial template file for each country that can be dynamically imported from the parent template:

*templates/langs/en.html*:
```
{% compress 'css' %}
<link rel="stylesheet" href="css/en.css">
{% endcompress %}
```

*templates/page.html*:
```
{% with %}
{% set country_code = some_function_that_guess_country_for_example() %}
{% include "langs/"+country_code+".html" %}
{% endwith %}
```

This way the separate template files can be pre-compressed and included dynamically.