Markup escape issues

[JakeStanger]

Describe the bug
#586 introduced Pango support to more places. In some places, the text needs to be (intelligently) escaped, as it is now causing blank strings and GTK warnings.

To Reproduce
Steps to reproduce the behavior:

1. Add the music module with default settings
2. Play a song with an & in its title (or where the artist has an &)
3. Observe GTK warning

Expected behavior

The & is correctly escaped. Markup continues to work as expected.

Additional context

Glib offers a markup_escape_text which will correctly escape Pango markup. This cannot be used on the full string as this then...escapes the markup.