Florian Müllner authored Sep 06, 2018 and Jonas Ådahl committed Sep 17, 2018

Commit dbf99330 moved all inline D-Bus interface descriptions to template
strings so we can stop escaping line breaks.

Unfortunately that unveiled a grave bug in xgettext, which currently cannot
handle files that contain both backtick and slash characters - as a result,
translations from affected files have started to disappear as translators
run xgettext/msgmerge.

Instead of reverting the change and getting the crusty escaping back, we
will take this as an opportunity to stop inlining the XML altogether and
load it from a resource instead.

To facilitate that, add a small helper method that loads a D-Bus interface
description from a dedicated resource bundle.

#537