[WIP] Automatic gettext calls on static texts in HAML

The **haml-magic-translations** gem automatically calls `_()` on all static texts in HAML files.
For string extraction see: https://github.com/potager/haml-magic-translations#extracting-strings-and-merging-translations
@skateman Similar comments as @Fryguy, why are we writing our own parse_tag?  It's ok to do it, but we should really say WHY so we can remove it later when it's no longer needed.

Is parse_tag a public method and safe to call `super` on the superclass?