calendar: Fix quoting issues in notification titles

Markup in notification titles is not support (and never has been).
Therefore the text is run through g_markup_escape_text(), and as
a result we do have to use markup internally to correctly show
legal-but-escape characters like '&' or '"'.

https://bugzilla.gnome.org/show_bug.cgi?id=744894

js/ui/calendar.js

@@ -1049,7 +1049,7 @@ const Message = new Lang.Class({
 
     setTitle: function(text) {
         let title = text ? _fixMarkup(text.replace(/\n/g, ' '), false) : '';
-        this.titleLabel.text = title;
+        this.titleLabel.clutter_text.set_markup(title);
     },
 
     setBody: function(text) {