Use fixed paths for welcome screen translations

This is a fix for #2317 (closed) (this merge request is specific to trunk and can not be cherry-picked to 1.1.x)

What it does is creates a new GtkImage over the existing one, this image is set to an svg containing the English version of the welcome text. It's set to translatable and has a comment directing translators what to do, the result is that a properly translated filename and the creation of a translated welcome text layer should provide the designs we want along with none of the problems with fonts, sizes and HiDPI prbles we see in the beta1.

The other advantage this gives us is allowing translators to tailor the way the text is shown in their language, or even change fonts to one that is better for them.

Example using Japanese, putting the test vertically: