CASE: use default for translations

You can now use default for translation-tags, where the default will be used when working in a language that doesn’t have a translation-tag.

Example:

{% comment %}Some translations{% endcomment %}
{% t= "t_alarmbelprocedure" nl:"De alarmbelprocedure is van toepassing." en:"The alarmbelprocedure is applicable." default:"The alarmbelprocedure is applicable." %}

{% t "t_alarmbelprocedure" %}

So when I would work in French, the translation would read The alarmbelprocedure is applicable. which is the default.